From Wikipedia, the free encyclopedia.
Eighty-one (81) is the natural number following eighty and preceeding eighty-two.
| 81 | |
|---|---|
| Cardinal | eighty-one |
| Ordinal | eighty-first |
| Numeral system | |
| Factorization | |
| Roman numeral | LXXXI |
| Binary | 01010001 |
| Hexadecimal | 51 |
Its factors are 1, 3, 9, 27, 81.
81 is:
- the atomic number of thallium (Tl)
- the title of a short film by Stephen Burke: 81
- the model number of: Unterseeboot 81, Sinclair ZX81
- the Messier number of the M81 Group of galaxies
- the number of the French department Tarn
- the designation of Interstate 81, a freeway that runs from Tennessee to New York.
- the code for international direct dial phone calls to Japan
- the year AD 81 or AD 1981.
80 and 82
