Prime Number Checker
Check if a number is prime, and see its factors and prime factorization.
Works for whole numbers up to 1,000,000,000,000.
About the Prime Number Checker
A prime number has exactly two divisors — 1 and itself. The AlarmDaddy Prime Number Checker tells you instantly whether a whole number is prime or composite, lists all of its factors (divisors), and breaks it into its prime factorization. It is handy for homework, cryptography basics, and simplifying fractions.
Enter any whole number up to a trillion. If it is composite, you will see every divisor and the unique product of primes that makes it up — for example 60 = 2² × 3 × 5. If it is prime, the tool confirms it has no divisors other than 1 and itself.
How to use this calculator
- 1Enter a whole number (up to 1,000,000,000,000).
- 2See whether it is prime or composite.
- 3Read its factors and prime factorization.
The formula
The checker tests divisibility only up to the square root of the number, because any larger factor pairs with a smaller one already tested. Prime factorization repeatedly divides out the smallest prime factor until nothing remains.