Prime Number Checker
Check multiple whole numbers up to 2^64 − 1 with exact integer arithmetic. Optionally obtain bounded prime factorization and see any composite cofactor that remains unresolved.
Your result
How the calculation works
Small-prime division is followed by Miller–Rabin using bases 2, 325, 9375, 28178, 450775, 9780504 and 1795265022, deterministic for integers below 2^64. Factorization uses trial division up to 100,000, then checks the remaining cofactor.
Worked example
97 is prime. 100 is composite with factors 2 × 2 × 5 × 5. Zero and one are neither prime nor composite.
Assumptions and limitations
Maximum 50 integers per batch. A primality result is deterministic within the supported range. Factorization is deliberately bounded: a remaining composite cofactor is shown as unresolved, never reported as a prime factor.
Paste one ordinary decimal integer per line. This tool is for arithmetic exploration and does not generate cryptographic keys or establish that an input is suitable for cryptographic use.
Method reviewed 2026-10-08. Calculation standards · Report an issue