Prime number checker
Enter any whole number and instantly see whether it is prime. A prime number is a whole number greater than 1 that is divisible only by 1 and itself. When a number is not prime, this tool also shows its prime factorisation — the unique set of prime factors that multiply to give it.
The check uses an efficient trial-division test up to the square root of your number, all in your browser, so nothing you enter is ever uploaded.