Free Online Prime Number Checker
Check if any number is prime. Find factors, prime factorization, and nearby prim...Check if any number is prime. Find factors, prime factorization, and nearby primes instantly. Works with large numbers up to 9 quadrillion.
Checker Features
Why Use Free Online Prime Number Checker?
Instant Primality Test
Check if any number is prime or composite with instant results using trial division.
Prime Factorization
See the complete prime factorization of any composite number.
All Factors
View all divisors/factors of the number, not just prime factors.
Nearby Primes
Navigate to the next or previous prime number with one click.
Check History
See your recent checks color-coded as prime (green) or composite (red).
100% Private
All calculations happen in your browser. No data is sent to any server.
Common Uses for Prime Checker
Math Education
Learn about prime numbers, factorization, and number theory concepts.
Programming
Verify primality algorithms and test edge cases in your code.
Cryptography
Understand prime numbers used in RSA encryption and security protocols.
Number Theory
Explore mathematical properties and relationships between numbers.
How It Works
Enter a Number
Type any positive integer in the input field, or use the quick check buttons for common numbers.
Check the Result
Click 'Check Number' or press Enter to see if the number is prime or composite with full factorization.
Explore Nearby Primes
Use the Previous/Next Prime buttons to navigate through prime numbers near your input.
Tips & Information
Quick Navigation
Use the Previous/Next Prime buttons to quickly explore sequences of prime numbers.
Pattern Recognition
All primes greater than 3 are of the form 6k +/- 1. Check numbers near multiples of 6 to find primes efficiently.
Large Numbers
For very large numbers, the check may take a moment. The tool handles numbers up to JavaScript's safe integer limit.