Prime Number Checker
Enter any non-negative whole number to find out whether it is prime. If it is composite, the tool shows its prime factorization and full list of divisors using efficient trial division up to the square root. Works on large integers and runs entirely in your browser.
Examples
84
Not prime — 2^2 × 3 × 7
How it works
The number is tested by trial division: it is divided by 2 and then by every odd number up to its square root. If none divides evenly, it is prime. No divisor larger than the square root needs checking, because it would have to pair with a smaller one already tried.
| Number | Result |
|---|---|
| 97 | Prime |
| 91 | Not prime: 7 × 13 |
| 84 | Not prime: 2^2 × 3 × 7 |
| 1 | Neither prime nor composite |
For a number that is not prime you also get its prime factorization and its divisors, with the first 24 listed when there are many. Whole numbers up to 9,007,199,254,740,991 are accepted; a very large prime near that limit takes tens of millions of divisions, so allow it a moment.
How to use Prime Number Checker
Why use this tool
Frequently asked questions
No. Zero and one are neither prime nor composite, and the tool labels them accordingly.
Any whole number up to JavaScript's safe integer limit (about 9 quadrillion) is supported via trial division.
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