Английская Википедия:84 (number)
Шаблон:Infobox number 84 (eighty-four) is the natural number following 83 and preceding 85.
In mathematics
84 is a semiperfect number,[1] being thrice a perfect number, and the sum of the sixth pair of twin primes <math>(41 + 43)</math>.[2]
It is the third (or second) dodecahedral number,[3] and the sum of the first seven triangular numbers (1, 3, 6, 10, 15, 21, 28, 36), which makes it the sixth tetrahedral number.[4]
The twenty-second unique prime in decimal, with notably different digits than its preceding (and known following) terms in the same sequence, contains a total of 84 digits.[5]
A hepteract is a seven-dimensional hypercube with 84 penteract 5-faces.
84 is the limit superior of the largest finite subgroup of the mapping class group of a genus <math>g</math> surface divided by <math>g</math>.Шаблон:Cn
Under Hurwitz's automorphisms theorem, a smooth connected Riemann surface <math>X</math> of genus <math>g > 1</math> will contain an automorphism group <math>\mathrm{Aut}(X) = G</math> whose order is classically bound to <math>|G| \le 84 \text { } (g - 1)</math>.[6]
There are 84 zero divisors in the 16-dimensional sedenions <math>\mathbb S</math>.[7]
In astronomy
- Messier object M84, a magnitude 11.0 lenticular galaxy in the constellation Virgo
- The New General Catalogue object NGC 84, a single star in the constellation Andromeda
In other fields
Eighty-four is also:
- The year AD 84, 84 BC, or 1984.
- The number of years in the Шаблон:Lang, a cycle used in the past by Celtic peoples,[8] equal to 3 cycles of the Julian Calendar and to 4 Metonic cycles and 1 octaeteris
- The atomic number of polonium
- The model number of Harpoon missile
- WGS 84 - The latest revision of the World Geodetic System, a fixed global reference frame for the Earth.
- The house number of 84 Avenue Foch
- The number of the French department Vaucluse
- The code for international direct dial phone calls to Vietnam
- The town of Eighty Four, Pennsylvania
- The company 84 Lumber
- The ISBN Group Identifier for books published in Spain
- A variation of the game 42 played with two sets of dominoes.
- The film 84 Charing Cross Road (1987) starring Anne Bancroft and Anthony Hopkins
- KKNX Radio 84 in Eugene, Oregon
- The B-Side to "Up All Night" (Take That song)
- British Army term for the 84mm Carl Gustav recoilless rifle.
- How many Earth years it takes Uranus to orbit the Sun once
- The total number of Vertcoin to be released is 84 million “Vertcoin”
- The number of former National Football League player Antonio Brown
See also
References
