Prime Number Finder & Factorizer

Test primality, factorise any integer into primes, sieve every prime in a range, look up the next or previous prime, and find the nth prime. Up to 16-digit factorisation with Pollard's rho and deterministic Miller-Rabin primality to 25 digits. Live, in your browser, no upload.

Single-number check

Range sieve

List every prime in an inclusive range. Max 10,000,000.

n-th prime

Find the n-th prime, 1-indexed (1st = 2).

About

  • Primality: deterministic Miller-Rabin with the Sorenson–Webster witness set covers every integer below ~3.3 × 10²⁴.
  • Factorisation: trial division up to 10⁶ then Pollard's rho (Brent's variant) for harder composites. Exact for any input below 2⁵³.
  • Sieve: classical Sieve of Eratosthenes, byte-packed to hold 10 million odds in ~5 MB.
  • BigInt: all math uses native BigInt; 64-bit integers are factorised cleanly, larger integers up to 25 digits are tested for primality.
  • Privacy: every computation runs locally. Nothing is uploaded.