DocomintPrime Number Checker
Check whether a number is prime, and see its smallest factor if it isn't.
Tests primality by trial division up to the square root of the number — the standard efficient method for numbers in the everyday range — and, when a number isn't prime, shows its smallest factor so you can see exactly why.
Example: 97 checks as prime — nothing from 2 up to its square root (about 9.8) divides it evenly — while 91 checks as not prime, since 7 divides it evenly (91 = 7 × 13), a factor pair easy to miss by eye since 91 isn't obviously composite at a glance.
How it works
- Enter a whole number
- Press Check
- The result — prime or not, with a factor if not — appears instantly, on your device
Frequently asked questions
What makes a number prime?
A prime number is a whole number greater than 1 with exactly two divisors: 1 and itself. If any other number divides it evenly, it's composite, not prime.
Is 1 a prime number?
No. By definition, a prime number must have exactly two distinct divisors (1 and itself); 1 only has one divisor (itself), so it's classified as neither prime nor composite.
Is my numbers uploaded anywhere?
No — Prime Number Checker runs entirely in your browser using JavaScript/WebAssembly. Your numbers is never sent to a server.