Prime number checker
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- A prime has exactly two divisors: 1 and itself. Test every divisor up to √n = 9.8489.
- None divides 97, so it is prime.
| Inputs | Answer |
|---|---|
| Whole number to test: 97 | 97 is a prime number. |
| Whole number to test: 91 | 91 is not prime: 7 × 13. |
| Whole number to test: 2 | 2 is a prime number. |
| Whole number to test: 1000003 | 1,000,003 is a prime number. |
How to use it
A prime number has exactly two divisors, 1 and itself. To test a number n, check every divisor up to the square root of n: if none divides it exactly, n is prime. The calculator does this and, for a number that is not prime, shows the factor it found.
The first primes are 2, 3, 5, 7, 11, 13, 17, 19, 23 and 29. 2 is the only even prime.
Frequently asked questions
Is 97 prime?
Yes. No number from 2 to 9 divides it.
Is 91 prime?
No. 91 = 7 × 13.
Is 2 prime?
Yes, and it is the only even prime number.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.