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|Factorization||22 × 3 × 7|
|Divisors||1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84|
- the sum of the first seven triangular numbers (making it a tetrahedral number).
- 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.
- 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 Insular latercus, a cycle used in the past by Celtic peoples, 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