Prime Number Checker
Test primality and get the full prime factorisation. Check whether any number is prime and see its prime factorisation instantly. Also shows the nearest primes above and below. Free prime checker.
About the Prime Number Checker
A prime number has exactly two divisors: 1 and itself. This checker tests any integer up to the trillions using trial division against candidate factors — with the optimisation of testing only 2, 3 and numbers of the form 6k±1 — then reports whether the number is prime. If it is composite, you get the complete prime factorisation; either way you also see the nearest primes above and below, useful for hunting twin primes or classroom exercises.
How to use the Prime Number Checker
- Type any positive integer.
- The verdict appears instantly.
- If composite, read the prime factorisation.
- Check neighbouring primes to explore further.
Key features
- Instant prime or composite verdict
- Full prime factorisation for composites
- Nearest primes above and below
- Handles numbers up to 15 digits
Why is 1 not a prime number?
What is the fastest way to check small primes?
Related Math Calculators tools
More utilities from the same category.
Percentage Calculator
Three percentage problems solved: of, is-what-percent, and change.
Average Calculator
Mean, median, mode, range and standard deviation in one step.
GCD & LCM Calculator
Greatest common divisor and least common multiple of any numbers.
Factorial Calculator
Compute n! exactly — even for huge numbers — with digits count.
Logarithm Calculator
Compute logs in any base — 2, e, 10 or custom.
Exponent Calculator
Raise any number to any power, including negatives and fractions.