⚠️ Warning: This is a draft ⚠️

This means it might contain formatting issues, incorrect code, conceptual problems, or other severe issues.

If you want to help to improve and eventually enable this page, please fork RosettaGit's repository and open a merge request on GitHub.

A '''long prime''' (the definition that will be used here) are primes whose reciprocals (in decimal) have a ''period length'' of one less than the prime number (also expressed in decimal).

'''Long primes''' are also known as: ::* base ten cyclic numbers ::* full reptend primes ::* golden primes ::* long period primes ::* maximal period primes ::* proper primes

;Example: '''7''' is the first long prime, the reciprocal of seven is '''1''''''/''''''7''', which is equal to the repeating decimal fraction '''0.142857142857···

The length of the ''repeating'' part of the decimal fraction is six, (the underlined part) which is one less than the (decimal) prime number '''7'''.

Thus '''7''' is a long prime.

There are other (more) general definitions of a '''long prime''' which include wording/verbiage for bases other than ten.

;Task: :* Show all long primes up to '''500''' (preferably on one line). :* Show the number of long primes up to ''' 500''' :* Show the number of long primes up to ''' 1,000''' :* Show the number of long primes up to ''' 2,000''' :* Show the number of long primes up to ''' 4,000''' :* Show the number of long primes up to ''' 8,000''' :* Show the number of long primes up to '''16,000''' :* Show the number of long primes up to '''32,000''' :* Show the number of long primes up to '''64,000''' (optional) :* Show all output here.

;;;Also see: :* the Wikipedia webpage: [http://wikipedia.org/wiki/Full_reptend_prime full reptend prime]. :* the MathWorld webpage: [http://mathworld.wolfram.com/FullReptendPrime.html full reptend prime]. :* the OEIS webpage: [http://oeis.org/A001913 A1913].

## C

{{trans|Go}}

```#include <stdio.h>
#include <stdlib.h>

#define TRUE 1
#define FALSE 0

typedef int bool;

void sieve(int limit, int primes[], int *count) {
bool *c = calloc(limit + 1, sizeof(bool)); // composite = TRUE
// no need to process even numbers
int i, p = 3, p2, n = 0;
while (TRUE) {
p2 = p * p;
if (p2 > limit) break;
for (i = p2; i <= limit; i += 2 * p) c[i] = TRUE;
while (TRUE) {
p += 2;
if (!c[p]) break;
}
}
for (i = 3; i <= limit; i += 2) {
if (!c[i]) primes[n++] = i;
}
*count = n;
free(c);
}

// finds the period of the reciprocal of n
int findPeriod(int n) {
int i, r = 1, rr, period = 0;
for (i = 1; i <= n + 1; ++i) {
r = (10 * r) % n;
}
rr = r;
while (TRUE) {
r = (10 * r) % n;
period++;
if (r == rr) break;
}
return period;
}

int main() {
int i, prime, count = 0, index = 0, primeCount, longCount = 0;
int *primes, *longPrimes;
int numbers[] = {500, 1000, 2000, 4000, 8000, 16000, 32000, 64000};
int totals[8];
primes = calloc(6500, sizeof(int));
longPrimes = calloc(2500, sizeof(int));
sieve(64000, primes, &primeCount);
for (i = 0; i < primeCount; ++i) {
prime = primes[i];
if (findPeriod(prime) == prime - 1) {
longPrimes[longCount++] = prime;
}
}
for (i = 0; i < longCount; ++i) {
if (longPrimes[i] > numbers[index]) {
totals[index++] = count;
}
count++;
}
totals[7] = count;
printf("The long primes up to 500 are:\n");
printf("[");
for (i = 0; i < totals[0]; ++i) {
printf("%d ", longPrimes[i]);
}
printf("\b]\n");

printf("\nThe number of long primes up to:\n");
for (i = 0; i < 8; ++i) {
printf("  %5d is %d\n", numbers[i], totals[i]);
}
free(longPrimes);
free(primes);
return 0;
}
```

{{out}}

```
The long primes up to 500 are:
[7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499]

The number of long primes up to:
500 is 35
1000 is 60
2000 is 116
4000 is 218
8000 is 390
16000 is 716
32000 is 1300
64000 is 2430

```

## C#

{{works with|C sharp|7}}

```using System;
using System.Collections.Generic;
using System.Linq;

public static class LongPrimes
{
public static void Main() {
var primes = SomePrimeGenerator.Primes(64000).Skip(1).Where(p => Period(p) == p - 1).Append(99999);
Console.WriteLine(string.Join(" ", primes.TakeWhile(p => p <= 500)));
int count = 0, limit = 500;
foreach (int prime in primes) {
if (prime > limit) {
Console.WriteLine(\$"There are {count} long primes below {limit}");
limit *= 2;
}
count++;
}

int Period(int n) {
int r = 1, rr;
for (int i = 0; i <= n; i++) r = 10 * r % n;
rr = r;
for (int period = 1;; period++) {
r = (10 * r) % n;
if (r == rr) return period;
}
}
}

}
```

{{out}}

```
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499
There are 35 long primes below 500
There are 60 long primes below 1000
There are 116 long primes below 2000
There are 218 long primes below 4000
There are 390 long primes below 8000
There are 716 long primes below 16000
There are 1300 long primes below 32000
There are 2430 long primes below 64000
```

### The Functions

This task uses [http://www.rosettacode.org/wiki/Extensible_prime_generator#The_function Extensible Prime Generator (F#)]

```
// Return true if prime n is a long prime. Nigel Galloway: September 25th., 2018
let fN n g = let rec fN i g e l = match e with | 0UL                -> i
| _ when e%2UL = 1UL -> fN ((i*g)%l) ((g*g)%l) (e/2UL) l
| _                  -> fN i ((g*g)%l) (e/2UL) l
fN 1UL 10UL (uint64 g) (uint64 n)
let isLongPrime n=Seq.length (factors (n-1) |> Seq.filter(fun g->(fN n g)=1UL))=1

```

```
primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<500) |> Seq.filter isLongPrime |> Seq.iter(printf "%d ")

```

{{out}}

```
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

```
```
printfn "There are %d long primes less than 500" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<500) |> Seq.filter isLongPrime |> Seq.length)

```

{{out}}

```
There are 35 long primes less than 500

```
```
printfn "There are %d long primes less than 1000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<1000) |> Seq.filter isLongPrime |> Seq.length)

```

{{out}}

```
There are 60 long primes less than 1000

```
```
printfn "There are %d long primes less than 2000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<2000) |> Seq.filter isLongPrime |> Seq.length)

```

{{out}}

```
There are 116 long primes less than 2000

```
```
printfn "There are %d long primes less than 4000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<4000) |> Seq.filter isLongPrime|> Seq.length)

```

{{out}}

```
There are 218 long primes less than 4000

```
```
printfn "There are %d long primes less than 8000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<8000) |> Seq.filter isLongPrime |> Seq.length)

```

{{out}}

```
There are 390 long primes less than 8000

```
```
printfn "There are %d long primes less than 16000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<16000) |> Seq.filter isLongPrime |> Seq.length)

```

{{out}}

```
There are 716 long primes less than 16000

```
```
printfn "There are %d long primes less than 32000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<32000) |> Seq.filter isLongPrime |> Seq.length)

```

{{out}}

```
There are 1300 long primes less than 32000

```
```
printfn "There are %d long primes less than 64000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<64000) |> Seq.filter isLongPrime|> Seq.length)

```

{{out}}

```
There are 2430 long primes less than 64000

```
```
printfn "There are %d long primes less than 128000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<128000) |> Seq.filter isLongPrime|> Seq.length)

```

{{out}}

```
There are 4498 long primes less than 128000
Real: 00:00:01.294, CPU: 00:00:01.300, GC gen0: 27, gen1: 0

```
```
printfn "There are %d long primes less than 256000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<256000) |> Seq.filter isLongPrime|> Seq.length)

```

{{out}}

```
There are 8434 long primes less than 256000
Real: 00:00:03.434, CPU: 00:00:03.440, GC gen0: 58, gen1: 0

```
```
printfn "There are %d long primes less than 512000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<512000) |> Seq.filter isLongPrime|> Seq.length)

```

{{out}}

```
There are 15920 long primes less than 512000
Real: 00:00:09.248, CPU: 00:00:09.260, GC gen0: 128, gen1: 0

```
```
printfn "There are %d long primes less than 1024000" (primes |> Seq.skip 3 |> Seq.takeWhile(fun n->n<1024000) |> Seq.filter isLongPrime|> Seq.length)

```

{{out}}

```
There are 30171 long primes less than 1024000
Real: 00:00:24.959, CPU: 00:00:25.020, GC gen0: 278, gen1: 1

```

## Factor

```USING: formatting fry io kernel math math.functions math.primes
math.primes.factors memoize prettyprint sequences ;
IN: rosetta-code.long-primes

: period-length ( p -- len )
[ 1 - divisors ] [ '[ 10 swap _ ^mod 1 = ] ] bi find nip ;

MEMO: long-prime? ( p -- ? ) [ period-length ] [ 1 - ] bi = ;

: .lp<=500 ( -- )
500 primes-upto [ long-prime? ] filter
"Long primes <= 500:" print [ pprint bl ] each nl ;

: .#lp<=n ( n -- )
dup primes-upto [ long-prime? t = ] count swap
"%-4d long primes <= %d\n" printf ;

: long-primes-demo ( -- )
.lp<=500 nl
{ 500 1,000 2,000 4,000 8,000 16,000 32,000 64,000 }
[ .#lp<=n ] each ;

MAIN: long-primes-demo
```

{{out}}

```
Long primes <= 500:
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

35   long primes <= 500
60   long primes <= 1000
116  long primes <= 2000
218  long primes <= 4000
390  long primes <= 8000
716  long primes <= 16000
1300 long primes <= 32000
2430 long primes <= 64000

```

## FreeBASIC

```' version 01-02-2019
' compile with: fbc -s console

Dim Shared As UByte prime()

Sub find_primes(n As UInteger)

ReDim prime(n)
Dim As UInteger i, k

' need only to consider odd primes, 2 has no repetion
For i = 3 To n Step 2
If prime(i) = 0 Then
For k = i * i To n Step i + i
prime(k) = 1
Next
End If
Next

End Sub

Function find_period(p As UInteger) As UInteger
' finds period for every positive number
Dim As UInteger period, r = 1

Do
r = (r * 10) Mod p
period += 1
If r <= 1 Then Return period
Loop

End Function

' ------=< MAIN >=------

#Define max 64000
Dim As UInteger p = 3, n1 = 3, n2 = 500, i, n50, count

find_primes(max)
Print "Long primes upto 500 are ";

For i = n1 To n2 Step 2
If prime(i) = 0 Then
If i -1 = find_period(i) Then
If n50 <= 50 Then
Print Str(i); " ";
End If
count += 1
End If
End If
Next

Print : Print

Do
Print "There are "; Str(count); " long primes upto "; Str(n2)

n1 = n2 +1
n2 += n2
If n1 > max Then Exit Do

For i = n1 To n2 Step 2
If prime(i) = 0 Then
If i -1 = find_period(i) Then
count += 1
End If
End If
Next
Loop

' empty keyboard buffer
While Inkey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End
```

{{out}}

```Long primes upto 500 are 7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

There are 35 long primes upto 500
There are 60 long primes upto 1000
There are 116 long primes upto 2000
There are 218 long primes upto 4000
There are 390 long primes upto 8000
There are 716 long primes upto 16000
There are 1300 long primes upto 32000
There are 2430 long primes upto 64000
```

## Go

```package main

import "fmt"

func sieve(limit int) []int {
var primes []int
c := make([]bool, limit+1) // composite = true
// no need to process even numbers
p := 3
for {
p2 := p * p
if p2 > limit {
break
}
for i := p2; i <= limit; i += 2 * p {
c[i] = true
}
for {
p += 2
if !c[p] {
break
}
}
}
for i := 3; i <= limit; i += 2 {
if !c[i] {
primes = append(primes, i)
}
}
return primes
}

// finds the period of the reciprocal of n
func findPeriod(n int) int {
r := 1
for i := 1; i <= n+1; i++ {
r = (10 * r) % n
}
rr := r
period := 0
for {
r = (10 * r) % n
period++
if r == rr {
break
}
}
return period
}

func main() {
primes := sieve(64000)
var longPrimes []int
for _, prime := range primes {
if findPeriod(prime) == prime-1 {
longPrimes = append(longPrimes, prime)
}
}
numbers := []int{500, 1000, 2000, 4000, 8000, 16000, 32000, 64000}
index := 0
count := 0
totals := make([]int, len(numbers))
for _, longPrime := range longPrimes {
if longPrime > numbers[index] {
totals[index] = count
index++
}
count++
}
totals[len(numbers)-1] = count
fmt.Println("The long primes up to 500 are: ")
fmt.Println(longPrimes[:totals[0]])

fmt.Println("\nThe number of long primes up to: ")
for i, total := range totals {
fmt.Printf("  %5d is %d\n", numbers[i], total)
}
}
```

{{out}}

```
The long primes up to 500 are:
[7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499]

The number of long primes up to:
500 is 35
1000 is 60
2000 is 116
4000 is 218
8000 is 390
16000 is 716
32000 is 1300
64000 is 2430

```

## J

```
NB. define the verb long
NB. long is true iff the prime input greater than 2
NB. is a rosettacode long prime.
NB. 0 is false, 1 is true.

long =: ( <:@:[ = #@~.@( [: }. ( | 10&* )^:( <@[ ) ) )&1&>

NB. demonstration of the long verb
NB. long applied to integers 3 through 9 inclusively

(,: long) 3 4 5 6 7 8 9
3 4 5 6 7 8 9
0 0 0 0 1 0 0

NB. find the number of primes through 64000

[ N =: p:^:_1 ] 64000
6413

NB. copy the long primes, excluding 2, the first.

LONG_PRIMES =: (#~ long) p: >: i. N

NB. those less than 500

( #~ <&500) LONG_PRIMES
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

NB. counts

[ MEASURE =: 500 * 2 ^ i. 8
500 1000 2000 4000 8000 16000 32000 64000

LONG_PRIMES ( ] ,: [: +/ </ ) MEASURE
500 1000 2000 4000 8000 16000 32000 64000
35   60  116  218  390   716  1300  2430

```

## Julia

{{trans|Sidef}}

```
using Primes

function divisors(n)
f = [one(n)]
for (p,e) in factor(n)
f = reduce(vcat, [f*p^j for j in 1:e], init=f)
end
return length(f) == 1 ? [one(n), n] : sort!(f)
end

function islongprime(p)
for i in divisors(p-1)
if powermod(10, i, p) == 1
return i + 1 == p
end
end
false
end

println("Long primes ≤ 500: ")
for i in 2:500
if islongprime(i)
i == 229 ? println(i) : print(i, "  ")
end
end
print("\n\n")

for i in [500, 1000, 2000, 4000, 8000, 16000, 32000, 64000]
println("Number of long primes ≤ \$i: \$(sum(map(x->islongprime(x), 1:i)))")
end

```

{{output}}

```
Long primes ≤ 500:
7  17  19  23  29  47  59  61  97  109  113  131  149  167  179  181  193  223  229
233  257  263  269  313  337  367  379  383  389  419  433  461  487  491  499

Number of long primes ≤ 500: 35
Number of long primes ≤ 1000: 60
Number of long primes ≤ 2000: 116
Number of long primes ≤ 4000: 218
Number of long primes ≤ 8000: 390
Number of long primes ≤ 16000: 716
Number of long primes ≤ 32000: 1300
Number of long primes ≤ 64000: 2430

```

## Kotlin

{{trans|Go}}

```// Version 1.2.60

fun sieve(limit: Int): List<Int> {
val primes = mutableListOf<Int>()
val c = BooleanArray(limit + 1)  // composite = true
// no need to process even numbers
var p = 3
while (true) {
val p2 = p * p
if (p2 > limit) break
for (i in p2..limit step 2 * p) c[i] = true
while (true) {
p += 2
if (!c[p]) break
}
}
for (i in 3..limit step 2) {
}
return primes
}

// finds the period of the reciprocal of n
fun findPeriod(n: Int): Int {
var r = 1
for (i in 1..n + 1) r = (10 * r) % n
val rr = r
var period = 0
while (true) {
r = (10 * r) % n
period++
if (r == rr) break
}
return period
}

fun main(args: Array<String>) {
val primes = sieve(64000)
val longPrimes = mutableListOf<Int>()
for (prime in primes) {
if (findPeriod(prime) == prime - 1) {
}
}
val numbers = listOf(500, 1000, 2000, 4000, 8000, 16000, 32000, 64000)
var index = 0
var count = 0
val totals = IntArray(numbers.size)
for (longPrime in longPrimes) {
if (longPrime > numbers[index]) {
totals[index++] = count
}
count++
}
totals[numbers.lastIndex] = count
println("The long primes up to 500 are:")
println(longPrimes.take(totals[0]))

println("\nThe number of long primes up to:")
for ((i, total) in totals.withIndex()) {
System.out.printf("  %5d is %d\n", numbers[i], total)
}
}
```

{{output}}

```
The long primes up to 500 are:
[7, 17, 19, 23, 29, 47, 59, 61, 97, 109, 113, 131, 149, 167, 179, 181, 193, 223, 229, 233, 257, 263, 269, 313, 337, 367, 379, 383, 389, 419, 433, 461, 487, 491, 499]

The number of long primes up to:
500 is 35
1000 is 60
2000 is 116
4000 is 218
8000 is 390
16000 is 716
32000 is 1300
64000 is 2430

```

## M2000 Interpreter

{{trans|Go}} Sieve leave to stack of values primes. This happen because we call the function as a module, so we pass the current stack (modules call modules passing own stack of values). We can place value to stack using Push to the top (as LIFO) or using Data to bottom (as FIFO). Variable Number read a number from stack and drop it.

```
Module LongPrimes {
Sieve=lambda (limit)->{
Flush
Buffer clear c as byte*limit+1
\\ no need to process even numbers
p=3
do
p2=p^2
if p2>limit then exit
i=p2
while i<=limit
Return c, i:=1
i+=2*p
end While
do
p+=2
Until not eval(c,p)
always
for i = 3 to limit step 2
if  eval(c,i) else data i
next i
}
findPeriod=lambda (n) -> {
r = 1
for i = 1 to n+1 {r = (10 * r) mod n}
rr = r : period = 0
do
r = (10 * r) mod n
period++
if r == rr then exit
always
=period
}
Call sieve(64000)  ' leave stack with primes
stops=(500,1000,2000,4000,8000,16000,32000,64000)
acc=0
stp=0
limit=array(stops, stp)
p=number  ' pop one
Print "Long primes up to 500:"
document lp500\$
for i=1 to 500
if i=p then
if findPeriod(i)=i-1 then acc++ :lp500\$=str\$(i)
p=number
end if
if empty then exit for
next i
lp500\$="]"
insert 1,1 lp500\$="["
Print lp500\$
Print
i=500
Print "The number of long primes up to:"
print i," is ";acc
stp++
m=each(stops,1,-2)
while m
for i=array(m)+1 to array(m,m^+1)
if i=p then
if findPeriod(i)=i-1 then acc++
p=number
end if
if empty then exit for
next i
print array(m,m^+1)," is ";acc
end While
}
LongPrimes

```

{{out}}

```
The long primes up to 500 are:
[7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499]

The number of long primes up to:
500 is 35
1000 is 60
2000 is 116
4000 is 218
8000 is 390
16000 is 716
32000 is 1300
64000 is 2430
</pre >

## Pascal

first post.old program modified. Using Euler Phi
www . arndt-bruenner.de/mathe/scripts/periodenlaenge.htm

```pascal

PROGRAM Periode;

{\$IFDEF FPC}
{\$MODE Delphi}

{\$OPTIMIZATION ON}
{\$OPTIMIZATION Regvar}
{\$OPTIMIZATION Peephole}
{\$OPTIMIZATION cse}
{\$OPTIMIZATION asmcse}
{\$else}
{\$Apptype Console}
{\$ENDIF}

uses
sysutils;

const
cBASIS = 10;
PRIMFELDOBERGRENZE = 6542;
{Das sind alle Primzahlen bis 2^16}
{Das reicht fuer al8le Primzahlen bis 2^32}
TESTZAHL = 500;//429496709;//High(Dword) DIV cBasis;
type
tPrimFeld = array [1..PRIMFELDOBERGRENZE] of Word;
tFaktorPotenz = record
Faktor,
Potenz  : DWord;
end;
//2*3*5*7*11*13*17*19*23  *29 > DWord also maximal 9 Faktoren
tFaktorFeld =  array [1..9] of TFaktorPotenz;//DWord
// tFaktorFeld =  array [1..15] of TFaktorPotenz;//QWord
tFaktorisieren = class(TObject)
private
fFakZahl   : DWord;
fFakBasis  : DWord;
fFakAnzahl : Dword;
fAnzahlMoeglicherTeiler : Dword;
fEulerPhi  : DWORD;
fStartPeriode : DWORD;
fPeriodenLaenge  : DWORD;
fTeiler    : array of DWord;
fFaktoren  : tFaktorFeld;
fBasFakt   : tFaktorFeld;
fPrimfeld  : tPrimFeld;

procedure PrimFeldAufbauen;
procedure Fakteinfuegen(var Zahl:Dword;inFak:Dword);
function  BasisPeriodeExtrahieren(var inZahl:Dword):DWord;
procedure NachkommaPeriode(var OutText: String);
public
function  Prim(inZahl:Dword):Boolean;
procedure AusgabeFaktorfeld(n : DWord);
procedure Faktorisierung (inZahl: DWord);
procedure TeilerErmitteln;
procedure PeriodeErmitteln(inZahl:Dword);
function  BasExpMod( b, e, m : Dword) : DWord;

property
property
property
end;

constructor tFaktorisieren.create;
begin
inherited;
PrimFeldAufbauen;

fFakZahl  := 0;
fFakBasis := cBASIS;
Faktorisierung(fFakBasis);
fBasFakt := fFaktoren;

fFakZahl := 0;
fEulerPhi := 1;
fPeriodenLaenge :=0;
fFakZahl := 0;
fFakAnzahl := 0;
fAnzahlMoeglicherTeiler := 0;
end;

function tFaktorisieren.Prim(inZahl:Dword):Boolean;
{Testet auf PrimZahl}
var
Wurzel,
pos       : Dword;
Begin
if fFakZahl = inZahl then
begin
result := (fAnzahlMoeglicherTeiler = 2);
exit;
end;
result := false;
if inZahl >1 then
begin
result := true;
Pos := 1;
Wurzel:= trunc(sqrt(inZahl));
While fPrimFeld[Pos] <= Wurzel do
begin
if (inZahl mod fPrimFeld[Pos])=0 then
begin
result := false;
break;
end;
inc(Pos);
IF Pos > High(fPrimFeld) then
break;
end;
end;
end;

Procedure tFaktorisieren.PrimFeldAufbauen;
{Baut die Liste der Primzahlen bis Obergrenze auf}
const
MAX = 65536;
var
TestaufPrim,
Zaehler,delta : Dword;

begin
Zaehler := 1;
fPrimFeld[Zaehler] := 2;
inc(Zaehler);
fPrimFeld[Zaehler] := 3;

delta := 2;
TestAufPrim:=5;
repeat
if prim(TestAufPrim) then
begin
inc(Zaehler);
fPrimFeld[Zaehler] := TestAufPrim;
end;
inc(TestAufPrim,delta);
delta := 6-delta; // 2,4,2,4,2,4,2,
until (TestAufPrim>=MAX);

end; {PrimfeldAufbauen}

procedure tFaktorisieren.Fakteinfuegen(var Zahl:Dword;inFak:Dword);
var
i : DWord;
begin
inc(fFakAnzahl);
with fFaktoren[fFakAnzahl] do
begin
fEulerPhi := fEulerPhi*(inFak-1);
Faktor :=inFak;
Potenz := 0;
while (Zahl mod inFak) = 0 do
begin
Zahl := Zahl div inFak;
inc(Potenz);
end;
For i := 2 to Potenz do
fEulerPhi := fEulerPhi*inFak;
end;
fAnzahlMoeglicherTeiler:=fAnzahlMoeglicherTeiler*(1+fFaktoren[fFakAnzahl].Potenz);
end;

procedure tFaktorisieren.Faktorisierung (inZahl: DWord);
var
j,
og : longint;
begin
if fFakZahl = inZahl then
exit;

fPeriodenLaenge := 0;
fFakZahl   := inZahl;
fEulerPhi  := 1;
fFakAnzahl := 0;
fAnzahlMoeglicherTeiler :=1;
setlength(fTeiler,0);

If inZahl < 2 then
exit;
og := round(sqrt(inZahl)+1.0);
{Suche Teiler von inZahl}
for j := 1 to High(fPrimfeld) do
begin
If fPrimfeld[j]> OG then
Break;
if (inZahl mod fPrimfeld[j])= 0 then
Fakteinfuegen(inZahl,fPrimfeld[j]);
end;
If inZahl>1 then
Fakteinfuegen(inZahl,inZahl);
TeilerErmitteln;
end; {Faktorisierung}

procedure tFaktorisieren.AusgabeFaktorfeld(n : DWord);
var
i :integer;
begin
if fFakZahl <> n then
Faktorisierung(n);
write(fAnzahlMoeglicherTeiler:5,' Faktoren ');

For i := 1 to fFakAnzahl-1 do
with fFaktoren[i] do
IF potenz >1 then
write(Faktor,'^',Potenz,'*')
else
write(Faktor,'*');
with fFaktoren[fFakAnzahl] do
IF potenz >1 then
write(Faktor,'^',Potenz)
else
write(Faktor);

writeln('  Euler Phi: ',fEulerPhi:12,PeriodenLaenge:12);
end;

procedure tFaktorisieren.TeilerErmitteln;
var
Position : DWord;
i,j : DWord;
procedure FaktorAufbauen(Faktor: DWord;n: DWord);
var
i,
Pot : DWord;
begin
Pot := 1;
i := 0;
repeat
IF n > Low(fFaktoren) then
FaktorAufbauen(Pot*Faktor,n-1)
else
begin
FTeiler[Position] := Pot*Faktor;
inc(Position);
end;
Pot := Pot*fFaktoren[n].Faktor;
inc(i);
until  i > fFaktoren[n].Potenz;
end;

begin
Position:= 0;
setlength(FTeiler,fAnzahlMoeglicherTeiler);
FaktorAufbauen(1,fFakAnzahl);
//Sortieren
For i := Low(fTeiler) to fAnzahlMoeglicherTeiler-2 do
begin
j := i;
while (j>=Low(fTeiler)) AND (fTeiler[j]>fTeiler[j+1]) do
begin
Position := fTeiler[j];
fTeiler[j] := fTeiler[j+1];
fTeiler[j+1]:= Position;
dec(j);
end;
end;
end;

function tFaktorisieren.BasisPeriodeExtrahieren(var inZahl:Dword):DWord;
var
i,cnt,
Teiler: Dword;
begin
cnt := 0;
result := 0;
For i := Low(fBasFakt) to High(fBasFakt) do
begin
with fBasFakt[i] do
begin
IF Faktor = 0 then
BREAK;
Teiler := Faktor;
For cnt := 2 to Potenz do
Teiler := Teiler*Faktor;
end;
cnt := 0;
while (inZahl<> 0) AND (inZahl mod Teiler = 0) do
begin
inZahl := inZahl div Teiler;
inc(cnt);
end;
IF cnt > result then
result := cnt;
end;
end;

procedure tFaktorisieren.PeriodeErmitteln(inZahl:Dword);
var
i,
TempZahl,
TempPhi,
TempPer,
TempBasPer: DWord;
begin
Faktorisierung(inZahl);
TempZahl := inZahl;
//Die Basis_Nicht_Periode ermitteln
TempBasPer := BasisPeriodeExtrahieren(TempZahl);
TempPer := 0;
IF TempZahl >1 then
begin
Faktorisierung(TempZahl);
TempPhi := fEulerPhi;
IF (TempPhi > 1) then
begin
Faktorisierung(TempPhi);
i := 0;
repeat
TempPer := fTeiler[i];
IF BasExpMod(fFakBasis,TempPer,TempZahl)= 1 then
Break;
inc(i);
until i >= Length(fTeiler);
IF i >= Length(fTeiler) then
TempPer := inZahl-1;
end;
end;

Faktorisierung(inZahl);
fPeriodenlaenge := TempPer;
fStartPeriode   := TempBasPer;
end;

procedure tFaktorisieren.NachkommaPeriode(var OutText: String);
var
i,
limit : integer;

Rest,
Rest1,
Divi,
basis: DWord;
pText : pChar;

procedure Ziffernfolge(Ende: longint);
var
j : longint;
begin
j := i-Ende;

while j < 0 do
begin
Rest := Rest *Basis;
Rest1:= Rest Div Divi;
Rest := Rest-Rest1*Divi;//== Rest1 Mod Divi

pText^ := chr(Rest1+Ord('0'));
inc(pText);

inc(j);
end;

i := Ende;
end;

begin
limit:= fStartPeriode+fPeriodenlaenge;

setlength(OutText,limit+2+2+5);
OutText[1]:='0';
OutText[2]:='.';
pText := @OutText[3];

Rest := 1;
Divi := fFakZahl;
Basis := fFakBasis;

i := 0;
Ziffernfolge(fStartPeriode);
if fPeriodenlaenge = 0 then
begin
setlength(OutText,fStartPeriode+2);
EXIT;
end;

pText^ := '_'; inc(pText);
Ziffernfolge(limit);
pText^ := '_'; inc(pText);

Ziffernfolge(limit+5);
end;

type
tZahl   = integer;
tRestFeld = array[0..31] of integer;

VAR
F : tFaktorisieren;

function tFaktorisieren.BasExpMod( b, e, m : Dword) : DWord;
begin
Result := 1;
IF m = 0 then
exit;
Result := 1;
while ( e > 0 ) do
begin
if (e AND 1) <> 0 then
Result :=  (Result * int64(b)) mod m;
b := (int64(b) * b ) mod m;
e := e shr 1;
end;
end;

procedure start;
VAR
Limit,
Testzahl : DWord;
longPrimCount  : int64;
t1,t0: TDateTime;
BEGIN

Limit := 500;
Testzahl := 2;
longPrimCount := 0;
t0 := time;

repeat
write(Limit:8,': ');
repeat
if F.Prim(Testzahl) then
begin
F.PeriodeErmitteln(Testzahl);
if F.PeriodenLaenge = Testzahl-1 then
Begin
inc(longPrimCount);
IF Limit = 500 then
write(TestZahl,',');
end
end;
inc(Testzahl);
until TestZahl = Limit;
inc(Limit,Limit);
write('  .. count ',longPrimCount:8,' ');
t1:= time;
If (t1-t0)>1/864000 then
write(FormatDateTime('HH:NN:SS.ZZZ',t1-T0));
writeln;
until Limit > 10*1000*1000;

t1 := time;
writeln;
writeln('count of long primes ',longPrimCount);
writeln('Benoetigte Zeit ',FormatDateTime('HH:NN:SS.ZZZ',T1-T0));

END;

BEGIN
F := tFaktorisieren.create;
writeln('Start');
start;
writeln('Fertig.');
F.free;
end.
```

{{out}}

```sh-4.4# ./Periode
Start
500: 7,17,19,23,29,47,59,61,97,109,113,131,149,167,179,181,193,223,229,233,257,263,269,313,337,367,379,383,389,419,433,461,487,491,499,  .. count       35
1000:   .. count       60
2000:   .. count      116
4000:   .. count      218
8000:   .. count      390
16000:   .. count      716
32000:   .. count     1300
64000:   .. count     2430
128000:   .. count     4498
256000:   .. count     8434 00:00:00.100
512000:   .. count    15920 00:00:00.220
1024000:   .. count    30171 00:00:00.494
2048000:   .. count    57115 00:00:01.140
4096000:   .. count   108381 00:00:02.578
8192000:   .. count   206594 00:00:06.073

count of long primes 206594
Benoetigte Zeit 00:00:06.073
Fertig.

```

## Perl

```use ntheory qw/divisors powmod is_prime/;

sub is_long_prime {
my(\$p) = @_;
return 0 unless is_prime(\$p);
for my \$d (divisors(\$p-1)) {
return \$d+1 == \$p if powmod(10, \$d, \$p)== 1;
}
0;
}

print "Long primes ≤ 500:\n";
print join(' ', grep {is_long_prime(\$_) } 1 .. 500), "\n\n";

for \$n (500, 1000, 2000, 4000, 8000, 16000, 32000, 64000) {
printf "Number of long primes ≤ \$n: %d\n",  scalar grep { is_long_prime(\$_) } 1 .. \$n;
}
```

{{out}}

```Long primes ≤ 500:
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

Number of long primes ≤ 500: 35
Number of long primes ≤ 1000: 60
Number of long primes ≤ 2000: 116
Number of long primes ≤ 4000: 218
Number of long primes ≤ 8000: 390
Number of long primes ≤ 16000: 716
Number of long primes ≤ 32000: 1300
Number of long primes ≤ 64000: 2430
```

### Using znorder

Faster due to going directly over primes and using znorder. Takes one second to count to 8,192,000.

```use ntheory qw/forprimes znorder/;
my(\$t,\$z)=(0,0);
forprimes {
\$z = znorder(10, \$_);
\$t++ if defined \$z && \$z+1 == \$_;
} 8192000;
print "\$t\n";
```

{{out}}

```206594
```

## Perl 6

{{works with|Rakudo|2018.06}} Not very fast as the numbers get larger.

```use Math::Primesieve;
my \$sieve = Math::Primesieve.new;

sub is-long (Int \$p) {
my \$r = 1;
my \$rr = \$r = (10 * \$r) % \$p for ^\$p;
my \$period;
loop {
\$r = (10 * \$r) % \$p;
++\$period;
last if \$period >= \$p or \$r == \$rr;
}
\$period == \$p - 1 and \$p > 2;
}

my @primes = \$sieve.primes(500);
my @long-primes = @primes.grep: {.&is-long};

put "Long primes ≤ 500:\n", @long-primes;

@long-primes = ();

for 500, 1000, 2000, 4000, 8000, 16000, 32000, 64000 -> \$upto {
state \$from = 0;
my @extend = \$sieve.primes(\$from, \$upto);
@long-primes.append: @extend.hyper(:8degree).grep: {.&is-long};
say "\nNumber of long primes ≤ \$upto: ", +@long-primes;
\$from = \$upto;
}
```

{{out}}

```Long primes ≤ 500:
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

Number of long primes ≤ 500: 35

Number of long primes ≤ 1000: 60

Number of long primes ≤ 2000: 116

Number of long primes ≤ 4000: 218

Number of long primes ≤ 8000: 390

Number of long primes ≤ 16000: 716

Number of long primes ≤ 32000: 1300

Number of long primes ≤ 64000: 2430
```

## Phix

Using primes and add_block from [[Extensible_prime_generator#Phix]]

```function is_long_prime(integer n)
integer r = 1, rr, period = 0
for i=1 to n+1 do
r = mod(10*r,n)
end for
rr = r
while true do
r = mod(10*r,n)
period += 1
if period>=n then return false end if
if r=rr then exit end if
end while
return period=n-1
end function
```

(use the same main() as below but limit maxN to 8 iterations)

Much faster version:

```function is_long_prime(integer n)
sequence f = factors(n-1,1)
integer count = 0
for i=1 to length(f) do
integer fi = f[i], e=1, base=10
while fi!=0 do
if mod(fi,2)=1 then
e = mod(e*base,n)
end if
base = mod(base*base,n)
fi = floor(fi/2)
end while
if e=1 then
count += 1
if count>1 then exit end if
end if
end for
return count=1
end function

procedure main()
atom t0 = time()
integer maxN = 500*power(2,14)--8)
while primes[\$]<maxN do
end while
sequence long_primes = {}
integer count = 0,
n = 500
for i=2 to length(primes) do    -- (skip 2)
integer prime = primes[i]
if is_long_prime(prime) then
if prime<500 then
long_primes &= prime
end if
if prime>n then
if n=500 then
printf(1,"The long primes up to 500 are:\n")
?long_primes
printf(1,"\nThe number of long primes up to:\n")
end if
printf(1,"  %7d is %d  (%s)\n", {n, count, elapsed(time()-t0)})
if n=maxN then exit end if
n *= 2
end if
count += 1
end if
end for
end procedure
main()
```

{{out}} slow version:

```
The long primes up to 500 are:
{7,17,19,23,29,47,59,61,97,109,113,131,149,167,179,181,193,223,229,233,257,263,269,313,337,367,379,383,389,419,433,461,487,491,499}

The number of long primes up to:
500 is 35  (0.2s)
1000 is 60  (0.3s)
2000 is 116  (0.3s)
4000 is 218  (0.6s)
8000 is 390  (1.5s)
16000 is 716  (4.9s)
32000 is 1300  (16.6s)
64000 is 2430  (1 minute and 01s)

```

fast version:

```
The long primes up to 500 are:
{7,17,19,23,29,47,59,61,97,109,113,131,149,167,179,181,193,223,229,233,257,263,269,313,337,367,379,383,389,419,433,461,487,491,499}

The number of long primes up to:
500 is 35  (0.2s)
1000 is 60  (0.2s)
2000 is 116  (0.2s)
4000 is 218  (0.2s)
8000 is 390  (0.2s)
16000 is 716  (0.3s)
32000 is 1300  (0.4s)
64000 is 2430  (0.7s)
128000 is 4498  (1.3s)
256000 is 8434  (2.8s)
512000 is 15920  (6.0s)
1024000 is 30171  (13.1s)
2048000 is 57115  (28.2s)
4096000 is 108381  (1 minute and 01s)
8192000 is 206594  (2 minutes and 11s)

```

## Python

{{trans|Kotlin}}

```def sieve(limit):
primes = []
c = [False] * (limit + 1) # composite = true
# no need to process even numbers
p = 3
while True:
p2 = p * p
if p2 > limit: break
for i in range(p2, limit, 2 * p): c[i] = True
while True:
p += 2
if not c[p]: break

for i in range(3, limit, 2):
if not c[i]: primes.append(i)
return primes

# finds the period of the reciprocal of n
def findPeriod(n):
r = 1
for i in range(1, n): r = (10 * r) % n
rr = r
period = 0
while True:
r = (10 * r) % n
period += 1
if r == rr: break
return period

primes = sieve(64000)
longPrimes = []
for prime in primes:
if findPeriod(prime) == prime - 1:
longPrimes.append(prime)
numbers = [500, 1000, 2000, 4000, 8000, 16000, 32000, 64000]
count = 0
index = 0
totals = [0] * len(numbers)
for longPrime in longPrimes:
if longPrime > numbers[index]:
totals[index] = count
index += 1
count += 1
totals[-1] = count
print('The long primes up to 500 are:')
print(str(longPrimes[:totals[0]]).replace(',', ''))
print('\nThe number of long primes up to:')
for (i, total) in enumerate(totals):
print('  %5d is %d' % (numbers[i], total))
```

{{out}}

```
The long primes up to 500 are:
[7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499]

The number of long primes up to:
500 is 35
1000 is 60
2000 is 116
4000 is 218
8000 is 390
16000 is 716
32000 is 1300
64000 is 2430

```

## Racket

{{trans|Go}} (at least '''find-period''')

```#lang racket
(require math/number-theory)

(define (find-period n)
(let ((rr (for/fold ((r 1))
((i (in-range 1 (+ n 2))))
(modulo (* 10 r) n))))
(let period-loop ((r rr) (p 1))
(let ((r′ (modulo (* 10 r) n)))
(if (= r′ rr) p (period-loop r′ (add1 p)))))))

(define (long-prime? n)
(and (prime? n) (= (find-period n) (sub1 n))))

(define memoised-long-prime? (let ((h# (make-hash))) (λ (n) (hash-ref! h# n (λ () (long-prime? n))))))

(module+ main
;; strictly, won't test 500 itself... but does it look prime to you?
(filter memoised-long-prime? (range 7 500 2))
(for-each
(λ (n) (displayln (cons n (for/sum ((i (in-range 7 n 2))) (if (memoised-long-prime? i) 1 0)))))
'(500 1000 2000 4000 8000 16000 32000 64000)))

(module+ test
(require rackunit)
(check-equal? (map find-period '(7 11 977)) '(6 2 976)))
```

{{out}}

```'(7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499)
(500 . 35)
(1000 . 60)
(2000 . 116)
(4000 . 218)
(8000 . 390)
(16000 . 716)
(32000 . 1300)
(64000 . 2430)
```

## REXX

For every '''doubling''' of the limit, it takes about roughly '''5''' times longer to compute the long primes.

### uses odd numbers

```/*REXX pgm calculates/displays base ten  long primes  (AKA golden primes, proper primes,*/
/*───────────────────── maximal period primes, long period primes, full reptend primes).*/
parse arg a                                      /*obtain optional argument from the CL.*/
if a='' | a=","  then a= '500 -500 -1000 -2000 -4000 -8000 -16000' ,  /*Not specified?  */
'-32000 -64000 -128000 -512000 -1024000'     /*Then use default*/
do k=1  for words(a);     H=word(a, k)       /*step through the list of high limits.*/
neg= H<1                                     /*used as an indicator to display count*/
H= abs(H)                                    /*obtain the absolute value of  H.     */
\$=                                           /*the list of  long primes   (so far). */
do j=7  to H  by 2                        /*start with 7,  just use odd integers.*/
if .len(j) + 1 \== j  then iterate        /*Period length wrong?   Then skip it. */
\$=\$ j                                     /*add the   long prime   to the \$ list.*/
end   /*j*/
say
if neg  then do;  say 'number of long primes ≤ '    H     " is: "     words(\$);    end
else do;  say   'list of long primes ≤ '    H":";         say strip(\$);    end
end      /*k*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
.len: procedure; parse arg x;  r=1;   do x;                   r= 10*r // x;     end  /*x*/
rr=r;   do p=1  until r==rr;    r= 10*r // x;     end  /*p*/
return p
```

{{out|output|text= when using the internal default inputs:}}

```
list of long primes ≤  500:
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499

number of long primes ≤  500  is:  35

number of long primes ≤  1000  is:  60

number of long primes ≤  2000  is:  116

number of long primes ≤  4000  is:  218

number of long primes ≤  8000  is:  390

number of long primes ≤  16000  is:  716

number of long primes ≤  32000  is:  1300

number of long primes ≤  64000  is:  2430

number of long primes ≤  128000  is:  4498

number of long primes ≤  512000  is:  15920

number of long primes ≤  1024000  is:  30171

```

===uses odd numbers, some prime tests=== This REXX version is about '''2''' times faster than the 1st REXX version (because it does some primality testing).

```/*REXX pgm calculates/displays base ten  long primes  (AKA golden primes, proper primes,*/
/*───────────────────── maximal period primes, long period primes, full reptend primes).*/
parse arg a                                      /*obtain optional argument from the CL.*/
if a='' | a=","  then a= '500 -500 -1000 -2000 -4000 -8000 -16000' ,  /*Not specified?  */
'-32000 -64000 -128000 -512000 -1024000'     /*Then use default*/
do k=1  for words(a);     H=word(a, k)       /*step through the list of high limits.*/
neg= H<1                                     /*used as an indicator to display count*/
H= abs(H)                                    /*obtain the absolute value of  H.     */
\$=                                           /*the list of  long primes   (so far). */
do j=7  to H  by 2;  parse var j '' -1 _  /*start with 7,  just use odd integers.*/
if     _==5  then iterate /*last digit a five?  Then not a prime.*/
if j// 3==0  then iterate /*Is divisible by  3?   "   "  "   "   */
if j\==11  then if j//11==0  then iterate /* "     "      " 11?   "   "  "   "   */
if j\==13  then if j//13==0  then iterate /* "     "      " 13?   "   "  "   "   */
if j\==17  then if j//17==0  then iterate /* "     "      " 17?   "   "  "   "   */
if j\==19  then if j//19==0  then iterate /* "     "      " 19?   "   "  "   "   */
if .len(j) + 1 \== j  then iterate        /*Period length wrong?   Then skip it. */
\$=\$ j                                     /*add the   long prime   to the \$ list.*/
end   /*j*/
say
if neg  then do;  say 'number of long primes ≤ '    H     " is: "     words(\$);    end
else do;  say   'list of long primes ≤ '    H":";         say strip(\$);    end
end      /*k*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
.len: procedure; parse arg x;  r=1;   do x;                   r= 10*r // x;     end  /*x*/
rr=r;   do p=1  until r==rr;    r= 10*r // x;     end  /*p*/
return p
```

{{out|output|text= is identical to the 1st REXX version.}}

### uses primes

This REXX version is about '''5''' times faster than the 1st REXX version (because it only tests primes).

```/*REXX pgm calculates/displays base ten  long primes  (AKA golden primes, proper primes,*/
/*───────────────────── maximal period primes, long period primes, full reptend primes).*/
parse arg a                                      /*obtain optional argument from the CL.*/
if a='' | a=","  then a= '500 -500 -1000 -2000 -4000 -8000 -16000' ,  /*Not specified?  */
'-32000 -64000 -128000 -512000 -1024000'     /*Then use default*/
m=0;            aa=words(a)                      /* [↑]  two list types of low primes.  */
do j=1  for aa;   m= max(m, abs(word(a, j))) /*find the maximum argument in the list*/
end   /*j*/
call genP                                        /*go and generate some primes.         */
do k=1  for aa;           H=word(a, k)       /*step through the list of high limits.*/
neg= H<1                                     /*used as an indicator to display count*/
H= abs(H)                                    /*obtain the absolute value of  H.     */
\$=                                           /*the list of  long primes   (so far). */
do j=7  to H  by 2
if \@.j               then iterate        /*Is  J  not a prime?    Then skip it. */
if .len(j) + 1 \== j  then iterate        /*Period length wrong?     "    "   "  */
\$=\$ j                                     /*add the   long prime   to the \$ list.*/
end   /*j*/                               /* [↑]  some pretty weak prime testing.*/
say
if neg  then do;  say 'number of long primes ≤ '    H     " is: "     words(\$);    end
else do;  say   'list of long primes ≤ '    H":";         say strip(\$);    end
end      /*k*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
genP: @.=0; @.2=1; @.3=1; @.5=1; @.7=1; @.11=1;   !.=0; !.1=2; !.2=3; !.3=5; !.4=7; !.5=11
#=5                                        /*the number of primes  (so far).      */
do g=!.#+2  by 2  until #>=m           /*gen enough primes to satisfy max  A. */
do d=2  until !.d**2 > g         /*only divide up to square root of  X. */
if g // !.d == 0  then iterate g /*Divisible?   Then skip this integer. */
end   /*d*/                      /* [↓]  a spanking new prime was found.*/
#=#+1;  @.g=1;  !.#=g                  /*bump P counter; assign P, add to P's.*/
end         /*g*/
return
/*──────────────────────────────────────────────────────────────────────────────────────*/
.len: procedure; parse arg x;  r=1;   do x;                   r= 10*r // x;     end  /*x*/
rr=r;   do p=1  until r==rr;    r= 10*r // x;     end  /*p*/
return p
```

{{out|output|text= is identical to the 1st REXX version.}}

## Ruby

Finding long prime numbers using finding period location (translation of Python's module def findPeriod(n))

```
require 'prime'

batas = 64_000 # limit number
start = Time.now # time of starting
lp_array = [] # array of long-prime numbers

def find_period(n)
r, period = 1, 0
(1...n).each {r = (10 * r) % n}
rr = r
loop do
r = (10 * r) % n
period += 1
break if r == rr
end
return period
end

Prime.each(batas).each do |prime|
lp_array.push(prime) if find_period(prime) == prime-1 && prime != 2
end

[500, 1000, 2000, 4000, 8000, 16000, 32000, 64000].each do |s|
if s == 500
puts "\nAll long primes up to  #{s} are: #{lp_array.count {|x| x < s}}. They are:"
lp_array.each {|x| print x, " " if x < s}
else
print "\nAll long primes up to #{s} are: #{lp_array.count {|x| x < s}}"
end
end

puts "\n\nTime: #{Time.now - start}"

```

{{out}}

```
All long primes up to  500 are: 35. They are:
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499
All long primes up to 1000 are: 60
All long primes up to 2000 are: 116
All long primes up to 4000 are: 218
All long primes up to 8000 are: 390
All long primes up to 16000 are: 716
All long primes up to 32000 are: 1300
All long primes up to 64000 are: 2430

Time: 27.085963

```

Alternatively, by using primitive way: converting value into string and make assessment for proper repetend position. Indeed produce same information, but with longer time.

```
require 'prime'
require 'bigdecimal'
require 'strscan'

batas = 64_000 # limit number
start = Time.now # time of starting
lp_array = [] # array of long-prime numbers
a = BigDecimal.new(1) # number being divided, that is 1.

Prime.each(batas).each do |prime|
cek = a.div(prime, (prime-1)*2).truncate((prime-1)*2).to_s('F')[2..-1] # Deviding 1 with prime and take its value as string.
if (cek[0, prime-1] == cek[prime-1, prime-1])
i = prime-2
until i < 5
break if cek[0, i] == cek[i, i]
i-=1
cek.slice!(-2, 2) # Shortening checked string to reduce checking process load
end

until i == 0
break if cek[0, (cek.size/i)*i].scan(/.{#{i}}/).uniq.length == 1
i-=1
end

lp_array.push(prime) if i == 0
end
end

[500, 1000, 2000, 4000, 8000, 16000, 32000, 64000].each do |s|
if s == 500
puts "\nAll long primes up to  #{s} are: #{lp_array.count {|x| x < s}}. They are:"
lp_array.each {|x| print x, " " if x < s}
else
print "\nAll long primes up to #{s} are: #{lp_array.count {|x| x < s}}"
end
end

puts "\n\nTime: #{Time.now - start}"

```

{{out}}

```
(same output with previous version, but longer time elapse)

Time: 1599.787375

```

## Sidef

The smallest divisor d of p-1 such that 10^d = 1 (mod p), is the length of the period of the decimal expansion of 1/p.

```func is_long_prime(p) {

for d in (divisors(p-1)) {
if (powmod(10, d, p) == 1) {
return (d+1 == p)
}
}

return false
}

say "Long primes ≤ 500:"
say primes(500).grep(is_long_prime).join(' ')

for n in ([500, 1000, 2000, 4000, 8000, 16000, 32000, 64000]) {
say ("Number of long primes ≤ #{n}: ", primes(n).count_by(is_long_prime))
}
```

{{out}}

```
Long primes ≤ 500:
7 17 19 23 29 47 59 61 97 109 113 131 149 167 179 181 193 223 229 233 257 263 269 313 337 367 379 383 389 419 433 461 487 491 499
Number of long primes ≤ 500: 35
Number of long primes ≤ 1000: 60
Number of long primes ≤ 2000: 116
Number of long primes ≤ 4000: 218
Number of long primes ≤ 8000: 390
Number of long primes ≤ 16000: 716
Number of long primes ≤ 32000: 1300
Number of long primes ≤ 64000: 2430

```

Alternatively, we can implement the ''is_long_prime(p)'' function using the `znorder(a, p)` built-in method, which is considerably faster:

```func is_long_prime(p) {
znorder(10, p) == p-1
}
```

## zkl

Using GMP (GNU Multiple Precision Arithmetic Library, probabilistic primes), because it is easy and fast to generate primes.

```var [const] BN=Import("zklBigNum");  // libGMP
primes,p := List.createLong(7_000), BN(3);  // one big alloc vs lots of allocs
while(p.nextPrime()<=64_000){ primes.append(p.toInt()) } // 6412 of them, skipped 2
primes.append(p.toInt());	// and one more so tail prime is >64_000

longPrimes:=primes.filter(fcn(p){ findPeriod(p)==p-1 }); // yawn
fcn findPeriod(n){
r,period := 1,0;
do(n){ r=(10*r)%n }
rr:=r;
while(True){   // reduce is more concise but 2.5 times slower
r=(10*r)%n;
period+=1;
if(r==rr) break;
}
period
}
```
```fiveHundred:=longPrimes.filter('<(500));
println("The long primes up to 500 are:\n",longPrimes.filter('<(500)).concat(","));

println("\nThe number of long primes up to:");
foreach n in (T(500, 1000, 2000, 4000, 8000, 16000, 32000, 64000)){
println("  %5d is %d".fmt( n, longPrimes.filter1n('>(n)) ));
}
```

{{out}}

```
The long primes up to 500 are:
7,17,19,23,29,47,59,61,97,109,113,131,149,167,179,181,193,223,229,233,257,263,269,313,337,367,379,383,389,419,433,461,487,491,499

The number of long primes up to:
500 is 35
1000 is 60
2000 is 116
4000 is 218
8000 is 390
16000 is 716
32000 is 1300
64000 is 2430

```