Prime Number Checker
Check whether an integer is prime, see its prime factorisation and find the nearest primes around it.
Number
Result
Enter an integer to analyse.
How it works
For numbers below 264, primality is decided exactly with a deterministic Miller–Rabin test. Larger inputs are checked with a probabilistic Miller–Rabin test (32 random rounds), so they are reported as probably prime rather than guaranteed. The input is limited to 200 digits. Factorisation uses trial division with a time limit, and the nearest-prime search is capped, so the page stays responsive on difficult inputs.