| ||||
|---|---|---|---|---|
| Cardinal | eighty-one | |||
| Ordinal | 81st (eighty-first) | |||
| Factorization | 34 | |||
| Divisors | 1, 3, 9, 27, 81 | |||
| Greek numeral | ΠΑ´ | |||
| Roman numeral | LXXXI | |||
| Binary | 10100012 | |||
| Ternary | 100003 | |||
| Senary | 2136 | |||
| Octal | 1218 | |||
| Duodecimal | 6912 | |||
| Hexadecimal | 5116 | |||
81 (eighty-one) is the natural number following 80 and preceding 82.