Yes, 139 is a prime number. Its only factors are 1 and 139.
A number is prime if no smaller prime up to its square root divides it. The square root of 139 is about 11.79, so it is enough to test the primes 2, 3, 5, 7 and 11.
| Divide by | Remainder | Divides evenly? |
|---|---|---|
| 2 | 1 | No |
| 3 | 1 | No |
| 5 | 4 | No |
| 7 | 6 | No |
| 11 | 7 | No |
None of them divides 139 evenly, so 139 is prime.
| Number | Prime? |
|---|---|
| 135 | No, 3 × 3 × 3 × 5 |
| 136 | No, 2 × 2 × 2 × 17 |
| 137 | Yes |
| 138 | No, 2 × 3 × 23 |
| 140 | No, 2 × 2 × 5 × 7 |
| 141 | No, 3 × 47 |
| 142 | No, 2 × 71 |
| 143 | No, 11 × 13 |
More about 139: factors of 139 · 139 squared · square root of 139 · 139 in binary · 139 in Roman numerals.
Another number? Use the prime number checker for any value, or see the list of prime numbers.