| 释义 |
- In mathematics
- In astronomy
- In other fields
- See also
- References
{{Infobox number
| number = 84
| divisor = 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84
}}84 (eighty-four) is the natural number following 83 and preceding 85. In mathematics 84 is: - the sum of the first seven triangular numbers (making it a tetrahedral number).[1]
- the sum of a twin prime (41 + 43).
- a semiperfect number, being thrice a perfect number.
- a palindromic number and a repdigit in bases 11 (7711), 13 (6613), 20 (4420), 27 (3327), and 41 (2241).
- the lim sup of the largest finite subgroup of the mapping class group of a genus g surface divided by g.
A hepteract is a seven-dimensional hypercube with 84 penteract 5-faces. 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 {{lang|la|Insular latercus}}, a cycle used in the past by Celtic peoples,[2] 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
See also- List of highways numbered 84
References1. ^{{Cite web|url=https://oeis.org/A000292|title=Sloane's A000292 : Tetrahedral numbers|last=|first=|date=|website=The On-Line Encyclopedia of Integer Sequences|publisher=OEIS Foundation|access-date=2016-05-29}}
2. ^{{cite book|author1=Bede|title=Ecclesiastical History of the English People |date=731|url=https://en.wikisource.org/wiki/Ecclesiastical_History_of_the_English_Nation_(Jane)/Book_2#2}}, 2.2, Latin original. See Easter controversy#Synod of Whitby in 664 and Computus.
{{Integers|zero}} 1 : Integers |