Prime Number Calculator
Check whether a number is prime.
Worth Knowing
A prime has exactly two divisors, 1 and itself, which is why 1 is not considered prime — it has only one divisor. To test a number you only need to check for factors up to its square root, since any factor larger than that pairs with a smaller one you'd have already found. Primes are the multiplicative building blocks of the integers, and their unpredictable distribution is what makes them the backbone of modern encryption.
How to Use
- Enter Number into the Prime Number Calculator above.
- Your result appears instantly as you type — there's no submit button or page reload.