81 (number)
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|---|---|---|---|---|
| Cardinal | eighty-one | |||
| Ordinal | 81st (eighty-first) |
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| Factorization | 34 | |||
| Divisors | 1, 3, 9, 27, 81 | |||
| Roman numeral | LXXXI | |||
| Binary | 10100012 | |||
| Ternary | 100003 | |||
| Quaternary | 11014 | |||
| Quinary | 3115 | |||
| Senary | 2136 | |||
| Octal | 1218 | |||
| Duodecimal | 6912 | |||
| Hexadecimal | 5116 | |||
| Vigesimal | 4120 | |||
| Base 36 | 2936 | |||
81 (eighty-one) is the natural number following 80 and preceding 82.
81 is:
The inverse of 81 is 0.012345679 recurring, missing only the digit "8" from the complete set of digits. This is an example of the general rule that, in base b,
omitting only the digit b−2.
Eighty-one is also:
The Arabic characters for the numerals 8 and 1 are visible in the left palm of the human hand. In China, 81 always reminds people People's Liberation Army as it was founded on August 1. 81 is used to refer to the motor-club Hell's Angels, since H and A are, respectively, the 8th and 1st letters of the alphabet.
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