Prime Number Checker
Check if a number is prime and find its factors.
About Prime Number Checker
Check whether a number is prime and see its factors if it is not. A prime number is a whole number greater than one that is divisible only by one and itself, and primes are foundational to number theory and cryptography. Enter any number and this tool instantly tells you whether it is prime, and if it is composite it shows the factors that divide it. It is a handy companion for students learning about divisibility, teachers preparing examples, and the simply curious. The test runs locally in your browser, so nothing you enter leaves your device, and the tool is completely free with no signup required.
How to use this tool
- 1Enter a whole number.
- 2See instantly whether it's prime.
- 3View its factors if it isn't.
Frequently asked questions
How large a number can it check?
It handles numbers up to JavaScript's safe integer limit using efficient trial division.
Is 1 a prime number?
No. By definition a prime has exactly two distinct divisors, so 1 is not prime.