Prime Number Checker
Check if a number is prime, with its factors and the nearest primes.
A prime number is a whole number greater than 1 whose only divisors are 1 and itself. For composite numbers, the prime factorization is shown. Runs in your browser.
Enter a whole number to check whether it's prime. If it isn't, you get its prime factorization (e.g. 84 = 2² × 3 × 7), and either way you see the previous and next prime numbers. Useful for math homework, cryptography study and curiosity. Runs in your browser.
How to use the Prime Number Checker
- Enter a whole number.
- See whether it's prime, with its prime factors if not.
- Check the previous and next prime numbers.
Frequently asked questions
What is a prime number?
A prime number is a whole number greater than 1 that has exactly two divisors: 1 and itself. 2, 3, 5, 7 and 11 are the first few. 1 is not prime.
What is prime factorization?
Writing a number as a product of prime numbers — for example 84 = 2 × 2 × 3 × 7, or 2² × 3 × 7. Every whole number above 1 has a unique prime factorization.