An integer greater than 1 is prime if its only positive integer divisors are 1 and itself. Otherwise, it is composite. Prime numbers are central elements of number theory, established as such by the fundamental theorem of arithmetic, which recognizes that all integers greater than 1 can be decomposed into unique products of primes. Wolfram|Alpha has many tools for working with primes and related ideas.
Check numbers for primality. Generate prime numbers or lists of prime numbers meeting certain conditions.