Prime Checker
Primality test and prime factorization.
600851475143 = 71 ร 839 ร 1471 ร 6857
Primality uses deterministic Miller-Rabin (correct for all n < 3.3ร10^24). Factorization is trial division, so huge semiprimes may stay unfactored.
About the Prime Checker
Test whether any integer up to 10^30 is prime using deterministic Miller-Rabin, which is provably correct for all numbers below 3.3 ร 10^24 with the chosen witness set. Composite numbers get a prime factorization by trial division, with repeated factors shown in exponent form like 2^3 ร 5.
How to use the Prime Checker
- Type a whole number โ commas, underscores and spaces are stripped automatically.
- Read the verdict tile: PRIME or Not prime, with the digit count.
- Open the Prime factorization line for composite inputs.
- Try the default 600851475143 to see a multi-factor composite in action.
Prime Checker FAQ
How reliable is the primality test?
It is deterministic Miller-Rabin with twelve fixed bases, proven correct for every input below about 3.3 ร 10^24 โ no probabilistic false positives in that range.
Why might factorization not finish?
Factoring uses trial division capped around ten million, so semiprimes made of two huge primes may show a leftover large factor noted as-is rather than split further.
Is any of this computation sent to a server?
No โ the test and factorization run entirely in your browser, so even very large numbers you paste stay on your machine.