Yes, 1,231 is a prime number. Its only factors are 1 and 1,231.
A number is prime if no smaller prime up to its square root divides it. The square root of 1,231 is about 35.09, so it is enough to test the primes 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 and 31.
| Divide by | Remainder | Divides evenly? |
|---|---|---|
| 2 | 1 | No |
| 3 | 1 | No |
| 5 | 1 | No |
| 7 | 6 | No |
| 11 | 10 | No |
| 13 | 9 | No |
| 17 | 7 | No |
| 19 | 15 | No |
| 23 | 12 | No |
| 29 | 13 | No |
| 31 | 22 | No |
None of them divides 1,231 evenly, so 1,231 is prime.
| Number | Prime? |
|---|---|
| 1,024 | No, 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 |
| 1,049 | Yes |
| 1,111 | No, 11 × 101 |
| 1,201 | Yes |
| 1,297 | Yes |
| 1,357 | No, 23 × 59 |
| 1,459 | Yes |
| 1,501 | No, 19 × 79 |
Another number? Use the prime number checker for any value, or see the list of prime numbers.