81 ( eighty-one ) is a natural number between 80 and 82 .
- 81 days a year - March 22 (in a leap year March 21 ).
| 81 | |
|---|---|
| Eighty-one | |
| ← 79 · 80 · 81 · 82 · 83 → | |
| Factorization | 3 4 |
| Roman notation | LXXXI |
| Binary | 1010001 |
| Octal | 121 |
| Hexadecimal | 51 |
Content
In Math
- 81 - is an odd compound [1] two-digit number.
- The sum of the digits of this number is 9
- The product of the digits of this number is 8
- Square of the number 81 - 6561
- Cube of the number 81 - 531 441
- 81 - the square of 9
- 81 - 4th power of 3
- 81 - the eighth open meander number [2] .
- 81 - the square of the sum of its numbers.
- Inversion 81 gives a periodic decimal fraction with a repetition of 0. 012345679 , where in the series of digits only "8" is missing. This is an example of a general rule, which for the base of the number system equal to b can be represented by the equation:
where the sequence is missing ( b −2).
In science
- Atomic number thallium .
In other areas
- 81 years old .
- 81 year BC e.
- 1981 year .
- ASCII -code character "Q".
- 81 - Code of the constituent entity of the Russian Federation and the Code of the State Traffic Safety Inspectorate-GAI of the Perm Territory .
- According to a single numbering of models of cars 81 - designation of subway cars ( 81-714, 81-717 , 81-540 and so on).
- 81 is the number of cells in the Japanese shogi chessboard.
- Absheron 81st Infantry Regiment .
- The 81st Guards Bomber Aviation Regiment is an aviation regiment of the USSR Armed Forces during World War II.
- The 81st separate air squadron of the Baltic Fleet Air Force is a military unit of the USSR armed forces in the Great Patriotic War.
- The 81st Infantry Division (1st formation) is the military unit of the USSR in the Great Patriotic War .
- The 81st Infantry Division (2nd formation) is the military unit of the USSR in the Great Patriotic War.
- The 81st Petraku Motorized Rifle Regiment is the Guards Motorized Rifle Regiment of the Armed Forces of the Russian Federation .
- 81st meridian of east longitude .
- 81st meridian of west longitude .
- The 81st parallel of north latitude .
- 81st parallel of south latitude .
- 81 km (platform) .
- 81 km - a village in the Volosovsky district of the Leningrad region .
See also
- 81st Army Corps (Germany) .
- 81-mm mortar system of captain Stokes .
- 81 Keith is a star in the constellation Keith .
- 81 Kita b (HD 16400 b) is an exoplanet ( gas planet ) orbiting the yellow giant 81 Kit.
- (81) Terpsichore - a large asteroid of the main asteroid belt .
- (81) Hells Angels - Digital designation of the first two letters of the American motorcycle club "Angels of Hell" (8 = H, 1 = A)]].
- 81 diver - anime and manga about shogi .
Notes
- ↑ sequence A002808 in OEIS
- ↑ sequence A005316 in OEIS