Determine whether an integer is prime

With Prime number test, students, teachers and analysts can verify a calculation during study or analysis. Determine whether an integer is prime.

Determine whether an integer is prime. Use it free in your browser without creating an account, then review the result before moving to the next step.

How to use

Enter the positive integer you want to test; it has to stay below 1,000,000,000.
Run the check and the answer tells you whether the number is prime.
If it is not prime, move on to a factor breakdown to see what divides it.
Clear the field to test the next value without reloading anything.

Example

The sample tests the number 91. Once the answer appears, read it as a yes or no: it says whether the value has divisors other than 1 and itself, and nothing more. Write the verdict down and continue with your exercise.

Input

Limits and formats

Only positive integers are accepted, and the value must stay below 1,000,000,000.
The answer is a plain yes or no; the smallest divisor of a composite number is never revealed.
Read the verdict twice if you plan to copy it into homework or a report.
With very large values, double check what you typed before trusting the response.

Where processing happens

The test is run by the page inside your browser, using only the integer you entered. That value does not leave your device and is not kept during or after your visit; the erase action takes it off the screen.

Frequently asked questions

Can 1 be considered a prime number?

No. A prime number has exactly two distinct divisors, 1 and itself, while 1 has only one. Enter a whole number of 2 or more if you want a meaningful answer from this test.

Can I check a whole list of numbers at once?

The field takes one value at a time. Work through your list entry by entry, clearing the box between tests so you do not mix up two results when you note them down.

How do I find the divisors instead of a yes or no?

This page answers only whether a number is prime. To see which numbers multiply together to give yours, use a prime factorisation rather than this test.