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[[Category:Mathematical operations]] [[Category:Classic CS problems and programs]] [[Category:Encyclopedia]] A '''prime number''' is defined as a positive integer which has exactly two factors: one and itself. A factor of a number is an integer which divides evenly into it--that is, divides with a remainder of zero. By this definition one and zero are not prime. One only has one factor (which is itself), and zero divided by any number always has a remainder of zero, so it effectively has an infinite number of factors.

Primality is frequently used for instructional purposes in computer science. Naive algorithms for calculating it are usually complex enough to be a test for a new programmer (barring algorithms built into languages), but simple enough that they can be used as parts of problems to follow.

Below is a list of tasks which involve the calculation or use of prime numbers.