Prime Number Checker

Check if a number is prime. Free online prime checker with divisibility analysis and next prime finder.

The Prime Number Checker determines whether any given number is prime or composite. Prime numbers—divisible only by 1 and themselves—are fundamental to mathematics and cryptography. Enter any positive integer to instantly discover if it's prime, see its factors if composite, and find the nearest prime numbers. Essential for number theory studies and mathematical exploration.

Common use cases

  • Number theory homework
  • Cryptography key generation
  • Mathematical research
  • Programming algorithm testing
  • Educational demonstrations

How to use

  1. Enter any positive integer
  2. Click check to analyze the number
  3. See if it's prime or composite
  4. View factors if not prime
  5. Find nearest prime numbers

FAQ

What is a prime number?

A prime number is greater than 1 and divisible only by 1 and itself. Examples: 2, 3, 5, 7, 11, 13...

Is 1 a prime number?

No, by mathematical convention, 1 is neither prime nor composite.

Is 2 the only even prime?

Yes, 2 is the only even prime number. All other even numbers are divisible by 2.

How does the checker work?

It tests divisibility by all numbers up to the square root of the input—if none divide evenly, it's prime.