Yes, 19 is a prime number. Its only factors are 1 and 19.
A number is prime if no smaller prime up to its square root divides it. The square root of 19 is about 4.36, so it is enough to test the primes 2 and 3.
| Divide by | Remainder | Divides evenly? |
|---|---|---|
| 2 | 1 | No |
| 3 | 1 | No |
None of them divides 19 evenly, so 19 is prime.
| Number | Prime? |
|---|---|
| 15 | No, 3 × 5 |
| 16 | No, 2 × 2 × 2 × 2 |
| 17 | Yes |
| 18 | No, 2 × 3 × 3 |
| 20 | No, 2 × 2 × 5 |
| 21 | No, 3 × 7 |
| 22 | No, 2 × 11 |
| 23 | Yes |
More about 19: factors of 19 · 19 squared · square root of 19 · 19 in binary · 19 in Roman numerals.
Another number? Use the prime number checker for any value, or see the list of prime numbers.