🔍 Prime Number Checker
Enter a whole number to find out if it is prime. If not, you get its prime factors.
Result
How the Prime Number Checker works
The number is tested by dividing it by every possible factor up to its square root. If none divide evenly, it is prime.
n is prime if it has no divisor d with 2 ≤ d ≤ √n
91 = 7 × 13 (not prime)
Step-by-step calculation
- 1Enter a whole number.
- 2Test divisors up to its square root.
- 3List prime factors if not prime.
Worked example
97 is prime. 91 is not: 91 = 7 × 13. 360 = 2³ × 3² × 5.
Prime Number Checker examples
| Whole number | Result |
|---|---|
| 49 | 49 is not prime |
| 73 | 73 is prime ✓ |
| 97 | 97 is prime ✓ |
| 121 | 121 is not prime |
| 146 | 146 is not prime |
Other inputs kept at the calculator's default values. Results calculated by this calculator.
Why use a Prime Number Checker?
Check primes and factor numbers for math and coding.
Important factors that can affect your results
- 1 is not prime.
- Very large numbers take longer.
- Negative numbers.
Frequently asked questions
Is 1 a prime number?
No. A prime has exactly two different factors, 1 and itself.
What is the only even prime?
2.
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Last reviewed November 2026 · How we build and check our tools · Report a problem