# 84 (number)

**84** (**eighty-four**) is the natural number following 83 and preceding 85.

| ||||
---|---|---|---|---|

Cardinal | eighty-four | |||

Ordinal | 84th (eighty-fourth) | |||

Factorization | 2^{2} × 3 × 7 | |||

Divisors | 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84 | |||

Greek numeral | ΠΔ´ | |||

Roman numeral | LXXXIV | |||

Binary | 1010100_{2} | |||

Ternary | 10010_{3} | |||

Quaternary | 1110_{4} | |||

Quinary | 314_{5} | |||

Senary | 220_{6} | |||

Octal | 124_{8} | |||

Duodecimal | 70_{12} | |||

Hexadecimal | 54_{16} | |||

Vigesimal | 44_{20} | |||

Base 36 | 2C_{36} |

## In mathematicsEdit

**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 (77
_{11}), 13 (66_{13}), 20 (44_{20}), 27 (33_{27}), and 41 (22_{41}). - 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 astronomyEdit

- 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 fieldsEdit

**Eighty-four** is also:

- The year AD
**84**, 84 BC, or 1984. - The number of years in the
*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 alsoEdit

## ReferencesEdit

**^**"Sloane's A000292 : Tetrahedral numbers".*The On-Line Encyclopedia of Integer Sequences*. OEIS Foundation. Retrieved 2016-05-29.**^**Bede (731).*Ecclesiastical History of the English People*., 2.2, Latin original. See Easter controversy#Synod of Whitby in 664 and Computus.