Check if a number is prime and find prime factorization
Type any positive integer and find out instantly whether it is prime. The tool also returns the prime factorization of composite numbers, so you see exactly which primes multiply together to produce the input.
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Calculate Greatest Common Divisor and Least Common Multiple of multiple numbers. Shows prime factorization and common divisors.
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You want to know whether 561 is prime, it "feels" prime but you are not sure.
Number
561
Result
Not prime · 561 = 3 × 11 × 17
561 looks prime but factors as 3 × 11 × 17, it is in fact a Carmichael number that fools naive primality tests, which is exactly why a real factorisation beats intuition. The tool returns the full prime factorisation, not just a yes/no.
Type any positive integer and find out instantly whether it is prime. The tool also returns the prime factorization of composite numbers, so you see exactly which primes multiply together to produce the input.
Quickly verify whether a number is prime and check factorizations.
Explore prime numbers and factorization, the foundation of RSA encryption.
The tool handles numbers up to several billion efficiently. Extremely large numbers may take a moment.
No. By mathematical convention, 1 is neither prime nor composite.
Every calculation runs locally in your browser. Your numbers and expressions are not transmitted or stored.