Prime Number Checker

A prime number is a whole number greater than 1 whose only divisors are 1 and itself. The first primes are 2, 3, 5, 7, 11 and 13. A whole number greater than 1 that is not prime is called composite.

No. A prime has exactly two different divisors, and 1 has only one. 0 and 1 are neither prime nor composite. 2 is the only even prime number.

Every whole number greater than 1 can be written as a product of primes in exactly one way. For example, 360 = 2³ × 3² × 5. Prime factorizations help you find the GCD and LCM, simplify fractions and count divisors.

It tries dividing by 2, by 3 and then by numbers of the form 6k ± 1, up to the square root of the number. If none of them divides it, the number is prime. Up to one trillion that is at most a few hundred thousand divisions, so the answer is instant.

Add 1 to each exponent in the prime factorization and multiply the results. 360 = 2³ × 3² × 5¹ has (3 + 1) × (2 + 1) × (1 + 1) = 24 divisors.