Prime Number Checker
Check if a number is prime and see all its factors.
What is a prime number checker?
A prime number checker tells you whether a number is prime and lists all of its factors. Enter any whole number and it checks whether anything divides it other than 1 and itself.
How to use the prime number checker
Enter a number and click Check. The checker shows whether the number is prime and lists its factors.
What is a prime number?
A prime number is a whole number greater than 1 that has exactly two factors: 1 and itself. For example, 2, 3, 5, 7, 11, 13 and 17 are prime. Numbers like 4, 6, 8 and 9 are not prime, because they have other factors.
Example
17 is prime. Its only factors are 1 and 17 — no other whole number divides it exactly.
Frequently Asked Questions
Is 17 a prime number?
Yes, 17 is prime. Its only factors are 1 and 17. Try it on the checker above.
Is 1 a prime number?
No. A prime number must have exactly two factors, but 1 has only one factor (itself), so it is not prime.
What are the first prime numbers?
The first prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29. Note that 2 is the only even prime number.
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