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 n ...

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 ot ...

φ(''x'') over the first sixteen integers. * a

semiperfect number In number theory, a semiperfect number or pseudoperfect number is a natural number ''n'' that is equal to the sum of all or some of its proper divisors. A semiperfect number that is equal to the sum of all its proper divisors is a perfect number. ...

, since adding up some subsets of its divisors (e.g., 1, 4, 5, 10, 20 and 40) gives 80. * a ménage number. *

palindromic A palindrome is a word, number, phrase, or other sequence of symbols that reads the same backwards as forwards, such as the words ''madam'' or ''racecar'', the date and time ''11/11/11 11:11,'' and the sentence: "A man, a plan, a canal – Pana ...

in bases 3 (2222₃), 6 (212₆), 9 (88₉), 15 (55₁₅), 19 (44₁₉) and 39 (22₃₉). * a

repdigit In recreational mathematics, a repdigit or sometimes monodigit is a natural number composed of repeated instances of the same digit in a positional number system (often implicitly decimal). The word is a portmanteau of repeated and digit. Example ...

in bases 3, 9, 15, 19 and 39. The

Pareto principle The Pareto principle states that for many outcomes, roughly 80% of consequences come from 20% of causes (the "vital few"). Other names for this principle are the 80/20 rule, the law of the vital few, or the principle of factor sparsity. Manage ...

(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 The 15 puzzle (also called Gem Puzzle, Boss Puzzle, Game of Fifteen, Mystic Square and many others) is a sliding puzzle having 15 square tiles numbered 1–15 in a frame that is 4 tiles high and 4 tiles wide, leaving one unoccupied tile position ...

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 ...

mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

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 for

cardinals Cardinal or The Cardinal may refer to: Animals * Cardinal (bird) or Cardinalidae, a family of North and South American birds **''Cardinalis'', genus of cardinal in the family Cardinalidae **''Cardinalis cardinalis'', or northern cardinal, the ...

to vote in

papal election A papal conclave is a gathering of the College of Cardinals convened to elect a Bishops in the Catholic Church, bishop of Rome, also known as the pope. Catholics consider the pope to be the Apostolic succession, apostolic successor of Saint ...

In other fields

Eighty is also: * used in the classic book title ''

Around the World in Eighty Days ''Around the World in Eighty Days'' (french: link=no, Le tour du monde en quatre-vingts jours) is an adventure novel by the French writer Jules Verne, first published in French in 1872. In the story, Phileas Fogg of London and his newly employe ...

'' * 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 Refo ...

or Dutch revolt (1568–1648) * the standard

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...

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 Ham ...

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 In photography and cinematography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a gl ...

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 oxidat ...

* The year

AD 80 __NOTOC__ AD 80 ( LXXX) was a leap year starting on Saturday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Domitianus (or, less frequently, year 833 ''Ab ur ...

80 BC __NOTOC__ Year 80 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Sulla and Metellus Pius (or, less frequently, year 674 ''Ab urbe condita''). The denomination 80 BC for this year has bee ...

, or 1980 * Eighty shilling ale * The older four-pin-base version of the 5Y3GT

rectifier A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...

tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a ...

* A common limit for the

characters per line In typography and computing, characters per line (CPL) or terminal width refers to the maximal number of monospaced characters that may appear on a single line. It is similar to line length in typesetting. History The limit of the line length ...

, 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 powe ...

has a song called " 80" * A fictional alien superhero named ''

Ultraman 80 is a Japanese tokusatsu TV show produced by Tsuburaya Productions which aired on the Tokyo Broadcasting System channel from April 2, 1980, to March 25, 1981, lasting a total of 50 episodes. After going off the air in 1981, the network still aired ...

'' * On the

Réaumur scale __NOTOC__ The Réaumur scale (; °Ré, °Re, °r), also known as the "octogesimal division", is a temperature scale for which the melting and boiling points of water are defined as 0 and 80 degrees respectively. The scale is named for René An ...

, 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 a ...

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 standardised g ...

References

External links

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