Yes, 181 is a prime number. Its only factors are 1 and 181.
A number is prime if no smaller prime up to its square root divides it. The square root of 181 is about 13.45, so it is enough to test the primes 2, 3, 5, 7, 11 and 13.
| Divide by | Remainder | Divides evenly? |
|---|---|---|
| 2 | 1 | No |
| 3 | 1 | No |
| 5 | 1 | No |
| 7 | 6 | No |
| 11 | 5 | No |
| 13 | 12 | No |
None of them divides 181 evenly, so 181 is prime.
| Number | Prime? |
|---|---|
| 177 | No, 3 × 59 |
| 178 | No, 2 × 89 |
| 179 | Yes |
| 180 | No, 2 × 2 × 3 × 3 × 5 |
| 182 | No, 2 × 7 × 13 |
| 183 | No, 3 × 61 |
| 184 | No, 2 × 2 × 2 × 23 |
| 185 | No, 5 × 37 |
More about 181: factors of 181 · square root of 181 · 181 in binary.
Another number? Use the prime number checker for any value, or see the list of prime numbers.