About this tool
Enter a whole number to find out whether it is prime and to see its prime factorization, such as 360 = 2^3 × 3^2 × 5. It uses trial division up to the square root, entirely in your browser.
Frequently asked questions
How big a number can I check?
Inputs are capped to a safe size so the page stays responsive. Very large numbers are rejected with a notice.
Is 1 prime?
No. By definition a prime has exactly two distinct divisors, so 0, 1 and negatives are not prime.