Type any positive whole number and find out immediately whether it is prime or composite. A prime number is greater than one and has no divisors other than one and itself, while a composite number can be split into smaller factors. This checker uses trial division up to the square root of your number, which is fast and exact even for large values, so you never wait and never get a wrong answer. When a number turns out to be composite, the tool also shows its smallest divisor so you can start factoring it by hand if you want. It is handy for cryptography homework, math practice, and quick fact checking. Everything runs locally in your browser, so nothing you type is sent anywhere.
A prime number is a whole number greater than 1 whose only divisors are 1 and itself. Numbers like 4, 6 and 9 are composite because they have other factors.
No. By the standard definition 1 is neither prime nor composite, and 2 is the smallest prime number.
When a number is composite the tool shows its smallest factor greater than 1, which is the first divisor found and a starting point for full factorization.
Type any positive whole number and find out immediately whether it is prime or composite. A prime number is greater than one and has no divisors other than one and itself, while a composite number can be split into smaller factors.
Yes. Prime Number Checker is completely free, with no sign-up and no usage limits.
Yes. Prime Number Checker runs in any modern web browser. There is nothing to download or install.
Yes. Prime Number Checker runs entirely on your device in your browser, so nothing you enter is uploaded to a server.