Number Theory Calculators

Prime Number Checker, Factor Finder, GCF and LCM Calculator, Factorial Calculator

Calculators for whole numbers: test a number for primality, list every factor and the prime factorisation, find the greatest common factor and least common multiple of a list, and work out factorials digit for digit.

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GCF Calculator

Greatest common factor of two or more numbers, with every step.

Every Number Theory tool

Factor Calculator

All the factors, factor pairs and prime factorisation of a number.

Factorial Calculator

Exact n factorial up to 5000!, with digits and trailing zeros.

GCF Calculator

Greatest common factor of two or more numbers, with every step.

LCM Calculator

Least common multiple of two or more numbers, with the working.

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Prime Factorisation Calculator

Prime factors of any number, with the division ladder shown.

Prime Number Checker

Check if a number is prime, or list the primes in a range.

Exact integers of any size

These tools use exact whole-number arithmetic, so a 25-digit number is tested for primality, and 100! is written out in full, without any rounding. The GCF and LCM accept as many numbers as you like and show the working for each answer.

Primes, factors and multiples

Primes and factors sit behind fraction simplifying, gear ratios, scheduling repeats and cryptography. The factor calculator lists every factor pair with the prime factorisation, the factorial calculator gives digit counts and trailing zeros, and the GCF and LCM pages explain clearly when you need each one and why.