84 (eighty-four) is the natural number following 83 and preceding 85.
| ||||
---|---|---|---|---|
Cardinal | eighty-four | |||
Ordinal | 84th (eighty-fourth) | |||
Factorization | 22 × 3 × 7 | |||
Divisors | 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42, 84 | |||
Greek numeral | ΠΔ´ | |||
Roman numeral | LXXXIV | |||
Binary | 10101002 | |||
Ternary | 100103 | |||
Senary | 2206 | |||
Octal | 1248 | |||
Duodecimal | 7012 | |||
Hexadecimal | 5416 |
In mathematics
84 is a semiperfect number,[1] being thrice a perfect number, and the sum of the sixth pair of twin primes .[2] It is the number of four-digit perfect powers in decimal.[3]
It is the third (or second) dodecahedral number,[4] and the sum of the first seven triangular numbers (1, 3, 6, 10, 15, 21, 28, 36), which makes it the sixth tetrahedral number.[5]
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.[6]
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 surface divided by .[citation needed]
Under Hurwitz's automorphisms theorem, a smooth connected Riemann surface of genus will contain an automorphism group whose order is classically bound to .[7]
84 is the thirtieth and largest for which the cyclotomic field has class number (or unique factorization), preceding 60 (that is the composite index of 84),[8] and 48.[9][10]
There are 84 zero divisors in the 16-dimensional sedenions .[11]
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 Insular latercus, a cycle used in the past by Celtic peoples,[12] 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