Prime Number Checker
Test any number and see its factors.
Result
Not prime
Factors: 1, 7, 13, 91
- Factors of 91: 1, 7, 13, 91.
- 91 is composite (more than two factors).
- Classic trap: 91 = 7 × 13, so it is not prime.
Formula
A prime has exactly two distinct positive factors: 1 and itself
How it works
Factors are listed for positive integers. 91 is a classic composite trap.
Common wrong answer
Calling 1 prime, or missing that 91 = 7 × 13.