Is the number 1 prime?
No. A prime number must be an integer greater than one with exactly two positive divisors.
Prime Number Checker
Check whether a positive integer is prime and find a divisor when it is not.
Calculations happen locally. We do not send your values to our server.
Example
Entering 97 reports that it is prime, while 91 is not prime because it is divisible by 7.
Calculation method
After handling two and even numbers, the checker tests odd divisors only up to the square root of the entered integer.
Important notes
The tool accepts integers from 2 through 1,000,000,000 and is not a proof system for cryptographic prime generation.
Frequently asked questions
Why stop testing at the square root?
Any larger factor of a composite number must be paired with a smaller factor already tested.
Can I test a decimal number?
No. Prime classification applies to integers, so decimals are rejected.