A prime number has exactly two divisors: 1 and itself. That definition is why 1 is not prime (it has only one divisor) and why 2 is the only even prime. To test a number n, it is enough to check divisibility by primes up to √n, because any larger factor would pair with a smaller one already checked. This checker tests the entered whole number for divisors and reports whether it is prime. It is useful for maths homework, number theory puzzles and coding exercises. It does not display a factorization, and this browser tool is not intended to generate or validate cryptographic primes.
Free, fast, and runs entirely in your browser — no signup, no upload to a server.