Prime Number Checker
Check whether any whole number is prime, even one with 40 digits, see its prime factorisation and find the nearest primes either side.
About this tool
A prime number is a whole number greater than 1 that can only be divided exactly by 1 and itself: 2, 3, 5, 7, 11 and so on. Every other whole number above 1 can be written as a product of primes in exactly one way, its prime factorisation, which is shown with powers, so 360 = 2³ × 3² × 5. The tool also tells you how many divisors the number has and the nearest primes on either side.
It works exactly on numbers of up to 40 digits, well beyond the 16-digit limit of ordinary calculators, using the Miller–Rabin primality test and Pollard's rho method for factorising. You can paste numbers with commas or spaces in them. Very large numbers made of two huge primes can be slow to split, and you'll be told if a factor couldn't be broken down in time.