Prime Number Checker
Check whether a number is prime, see its prime factors, and list the primes in a range.
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How to use
- Type a whole number to see whether it is prime and how it factors.
- Enter a range and press “List primes” to list every prime in it.
- Copy or download the list of primes.
How it works
Primality is checked with the deterministic Miller–Rabin test using the first twelve primes as witnesses, which gives a proven-correct answer for every number below 3.3 × 10²⁴. Factorization combines trial division with Pollard’s rho algorithm, and ranges use the sieve of Eratosthenes.
Limitations
- Prime checks work up to 10²⁴; factorization is shown up to 10¹⁸ so the page stays responsive.
- Ranges can go up to 10,000,000.
Privacy
Your text is processed entirely in this browser tab. Nothing is uploaded, logged or saved by this tool.
Local processing protects your data from being uploaded, but it cannot protect against a compromised device or malicious browser extensions.