Prime Number Checker

Find out if a number is prime. If it isn’t, see what divides it.

Whole numbers up to 10¹².
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How to Tell if a Number Is Prime

A prime has exactly two divisors, 1 and itself. To test n, try dividing by every prime up to √n; if none divide evenly, n is prime.

Worked Example

Tips

2 is the only even prime. The primes under 50 are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43 and 47.