80 (eighty) is the

natural number In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and ordering (as in "this is the ''third'' largest city in the country"). Numbers used for counting are called '' cardinal ...

following 79 and preceding 81.

In mathematics

80 is: * the sum of

Euler's totient function In number theory, Euler's totient function counts the positive integers up to a given integer that are relatively prime to . It is written using the Greek letter phi as \varphi(n) or \phi(n), and may also be called Euler's phi function. In ...

φ(''x'') over the first sixteen integers. * a semiperfect number, since adding up some subsets of its divisors (e.g., 1, 4, 5, 10, 20 and 40) gives 80. * a ménage number. * palindromic in bases 3 (2222₃), 6 (212₆), 9 (88₉), 15 (55₁₅), 19 (44₁₉) and 39 (22₃₉). * a repdigit in bases 3, 9, 15, 19 and 39. The Pareto principle (also known as the 80-20 rule) states that, for many events, roughly 80% of the effects come from 20% of the causes... Every solvable configuration of the 15 puzzle can be solved in no more than 80 single-tile moves.A. Brüngger, A. Marzetta, K. Fukuda and J. Nievergelt
The parallel search bench ZRAM and its applications
''Annals of Operations Research'' 90 (1999), pp. 45–63.

In science

* The

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...

of mercury

In religion

* According to Exodus 7:7, Moses was 80 years old when he initially spoke to Pharaoh on behalf of his people. Today, 80 years of age is the upper

age limit This article gives an outline of age restrictions. List * Age of candidacy *Age of consent * Age requirements in gymnastics * Age segregation * Defense of infancy * Legal drinking age *Legal smoking age * Legal working age * List of countri ...

for cardinals to vote in

papal election A papal conclave is a gathering of the College of Cardinals convened to elect a bishop of Rome, also known as the pope. Catholics consider the pope to be the apostolic successor of Saint Peter and the earthly head of the Catholic Church. ...

In other fields

Eighty is also: * used in the classic book title '' Around the World in Eighty Days'' * the length of the

Eighty Years' War The Eighty Years' War or Dutch Revolt ( nl, Nederlandse Opstand) ( c.1566/1568–1648) was an armed conflict in the Habsburg Netherlands between disparate groups of rebels and the Spanish government. The causes of the war included the Re ...

or Dutch revolt (1568–1648) * the standard TCP/IP

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as ...

number for

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, ...

connections * the 80A, 80B and 80C photographic filters correct for excessive redness under

tungsten lighting An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxida ...

* The year AD 80, 80 BC, or 1980 * Eighty shilling ale * The older four-pin-base version of the

5Y3GT The 5Y3 is a medium-power directly heated full-wave rectifier vacuum tube introduced by RCA in 1935. It has found wide use in tube radios and early guitar amplifiers (of the Fender Champ type). It is virtually identical, electrically, to the old ...

rectifier tube * A common limit for the characters per line, in computing, derived from the number of columns in IBM cards * American band

Green Day Green Day is an American rock band formed in the East Bay of California in 1987 by lead vocalist and guitarist Billie Joe Armstrong, together with bassist and backing vocalist Mike Dirnt. For most of the band's career, they have been a ...

has a song called " 80" * A fictional alien superhero named '' Ultraman 80'' * On the Réaumur scale, 80 degrees is the boiling temperature of pure

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...

References

External links

* wiktionary:eighty for ''80'' in other languages. {{DEFAULTSORT:80 (Number) Integers