Prime Number Checker
Is 97 prime — or 91? This free checker tells you instantly whether any number is prime or composite, shows all its factors, lists every prime up to N, and finds the next prime after your number.
Enter a number, the verdict will show here.
List Primes Up To N
Note: for the list, N is capped at 100,000 so the browser does not slow down. If you enter a larger N, the list will be made up to 100,000.
How to use
- Enter the number you want to check in the input box.
- See at once whether it is prime or composite, with its smallest factor and the full factor list.
- Enter N in the "Up to (N)" box to list all prime numbers up to N.
- Find the next prime number after the number you entered.
How it works
A prime number is only divisible by 1 and itself — like 2, 3, 5, 7, 11. The checker tests divisors up to the square root of the number; if a divisor is found the number is composite and the smallest factor is shown. The list uses the Sieve of Eratosthenes.
Example 1: 97 is prime — no number from 2 to 9 divides it fully.
Example 2: 91 is composite — 91 = 7 × 13, the smallest factor is 7, and the factors are 1, 7, 13, 91.