Prime Number Checker & Factorization
Check whether a number is prime and find its prime factorization, all divisors, and the nearest primes above and below.
How to use
- 1Enter a whole number (up to 9 quadrillion).
- 2See whether it's prime, its prime factors and its divisors.
How it's calculated
Trial division by 2 and odd numbers up to √n. The number of divisors = Π(eᵢ + 1) over the prime factorization.
Frequently asked questions
Is 1 a prime number?
No — a prime has exactly two distinct divisors, 1 and itself. 1 has only one.
What's the only even prime?
2. Every other even number is divisible by 2.
How large a number can I check?
Up to 9,007,199,254,740,991 (2⁵³ − 1). Very large numbers with big prime factors may take a moment.