| Next prime | 19 |
| Previous prime | 13 |
| Octal | (21)8 |
| Hexadecimal | (11)16 |
| Prime gap | 2 |
| 4th Twin prime (the small number) | The big number is 19 . |
| 5th Prime triplet (the smallest number) | The others are 19 and 23 . |
| 5th Sexy prime (the small number) | The big number is 23 . |
| 3rd Prime of the Form 4n+1 | 12 + 42 |
| 2nd Emirp (reversible prime) | |
| 3rd Fermat prime | 222 + 1 |
| 6th Left-truncatable prime |