TheInfoList

18 (eighteen) 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 total order, ordering (as in "this is the ''third'' largest city in the country"). In common mathematical terminology, w ...
following 17 and preceding 19.

# In mathematics

* Eighteen is a
composite number A composite number is a positive integer In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculu ...
, its
divisor In mathematics, a divisor of an integer n, also called a factor of n, is an integer m that may be multiplied by some integer to produce n. In this case, one also says that n is a multiple of m. An integer n is divisible or evenly divisible by ...

s being , , , and . Three of these divisors (3, 6 and 9) add up to 18, hence 18 is a
semiperfect number In number theory, a semiperfect number or pseudoperfect number is a natural number In mathematics, the natural numbers are those used for counting (as in "there are ''six'' coins on the table") and total order, ordering (as in "this is the '' ...
. Eighteen is the first inverted square-prime of the form ''p''·''q''2. * In
base ten The decimal numeral system (also called the base-ten positional numeral system, and occasionally called denary or decanary) is the standard system for denoting integer and non-integer numbers. It is the extension to non-integer numbers of the Hi ...
, it is a
Harshad number In mathematics, a harshad number (or Niven number) in a given number base is an integer that is divisible by the digit sum, sum of its digits when written in that base. Harshad numbers in base are also known as -harshad (or -Niven) numbers. Harsha ...
. * It is an
abundant number In number theory, an abundant number or excessive number is a number that is smaller than the sum of its proper divisors. The integer 12 is the first abundant number. Its proper divisors are 1, 2, 3, 4 and 6 for a total of 16. The amount by which ...
, as the sum of its proper divisors is greater than itself (1+2+3+6+9 = 21). It is known to be a solitary number, despite not being
coprime In number theory, two integer An integer (from the Latin wikt:integer#Latin, ''integer'' meaning "whole") is colloquially defined as a number that can be written without a Fraction (mathematics), fractional component. For example, 21, 4, 0, ...
to this sum. * It is the number of one-sided
pentomino Derived from the Greek word for '5', and "domino", a pentomino (or 5-omino) is a polyomino of order 5, that is, a polygon in the Plane (geometry), plane made of 5 equal-sized squares connected edge-to-edge. When rotation symmetry, rotations and r ...

es. * It is the only number where the sum of its written digits in
base 10 The decimal numeral system A numeral system (or system of numeration) is a writing system A writing system is a method of visually representing verbal communication Communication (from Latin ''communicare'', meaning "to share") is t ...

(1+8 = 9) is equal to half of itself (18/2 = 9).

# In science

## Chemistry

* Eighteen is the
atomic number 300px, The Rutherford–Bohr model of the hydrogen atom () or a hydrogen-like ion (). In this model it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one ...
of
argon Argon is a with the  Ar and  18. It is in group 18 of the and is a . Argon is the third-most abundant in the , at 0.934% (9340 ). It is more than twice as abundant as (which averages about 4000 ppmv, but varies greatly), 23 time ...

. *
Group A group is a number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with ...
18 of the
periodic table The periodic table, also known as the periodic table of (the) chemical elements, is a tabular display of the chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is ...

is called the
noble gases The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In ...
. * The 18-electron rule is a
rule of thumb ''Rule of thumb'' is an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the seventeenth century and has been associated with various trades where quantities we ...
in
transition metal In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations tha ...
chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a with other . ...

for characterising and predicting the stability of metal complexes.

# In religion and literature

* The
Hebrew Hebrew (, , or ) is a Northwest Semitic languages, Northwest Semitic language of the Afroasiatic languages, Afroasiatic language family. Historically, it is regarded as the language of the Israelites, Judeans and their ancestors. It is the o ...
word for "life" is חי ('' chai''), which has a
numerical value A number is a mathematical object used to count, measure, and label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers can b ...
of 18. Consequently, the custom has arisen in Jewish circles to give donations and monetary gifts in multiples of 18 as an expression of blessing for long life. * In
Judaism Judaism is an Abrahamic religions, Abrahamic, monotheism, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion ...
, in the
Talmud The Talmud (; he, תַּלְמוּד ''Tálmūḏ'') is the central text of Rabbinic Judaism and the primary source of Jewish religious law (''halakha'') and Jewish theology. Until the advent of modernity, in nearly all Jewish communities, the ...

;
Pirkei Avot Pirkei Avot ( he, פִּרְקֵי אָבוֹת; also transliterated as ''Pirkei Avoth'' or ''Pirkei Avos'' or ''Pirke Aboth''), which translates to English as Chapters of the Fathers, is a compilation of the ethics, ethical teachings and Maxim ( ...

(5:25), Rabbi Yehudah ben Teime gives the age of 18 as the appropriate age to get married (''"Ben shmonah esra lechupah"'', at eighteen years old to the
Chupah A ''chuppah'' ( he, חוּפָּה, pl. חוּפּוֹת, ''chuppot'', literally, "canopy" or "covering"), also huppah, chipe, chupah, or chuppa, is a canopy under which a Jewish Jews ( he, יְהוּדִים ISO 259-2ISO The Inte ...
(marriage canopy)). (See
Coming of age Coming of age is a young person Youth is the time of life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining processes, from those t ...
,
Age of majority The age of majority is the threshold of adulthood as recognized or declared in law. It is the moment when minor Minor may refer to: * Minor (law), a person under the age of certain legal activities. ** A person who has not reached the age of ...

). * Shemoneh Esrei (sh'MOH-nuh ES-ray) is a prayer that is the center of any Jewish religious service. Its name means "eighteen". The prayer is also known as the Amidah. * In
Ancient Roman In historiography, ancient Rome is Roman people, Roman civilization from the founding of the Italian city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom (753 BC ...
custom the number 18 can symbolise a blood relative. *
Joseph Heller Joseph Heller (May 1, 1923 – December 12, 1999) was an American author of novels, short stories, plays, and screenplays. His best-known work is the 1961 novel ''Catch-22 ''Catch-22'' is a satirical war novel by American author Joseph Hell ...

's novel ''
Catch-22 ''Catch-22'' is a satirical Satire is a genre Genre () is any form or type of communication in any mode (written, spoken, digital, artistic, etc.) with socially-agreed-upon conventions developed over time. In popular usage, it normall ...
'' was originally named ''Catch-18'' because of the Hebrew meaning of the number, but was amended to the published title to avoid confusion with another war novel,
Mila 18 ''Mila 18'' is a novel by Leon Uris Leon Marcus Uris (August 3, 1924 – June 21, 2003) was an American author of historical fiction who wrote many bestselling books including '' Exodus'' (published in 1958) and '' Trinity'' (published in 197 ...
.N James. ''The Early Composition History of Catch-22''. In Biographies of Books: The Compositional Histories of Notable American Writings, J Barbour, T Quirk (edi.) pp. 262-90. Columbia:
University of Missouri Press The University of Missouri Press is a university press 200px, The Pitt Building in Cambridge, which used to be the headquarters of Cambridge University Press, and now serves as a conference centre for the Press. A university press is an academic p ...
, 1996
* There are 18 chapters in the
Bhagavad Gita The ''Bhagavad Gita'' (; sa, भगवद्गीता।, IAST The International Alphabet of Sanskrit Transliteration (IAST) is a transliteration scheme that allows the lossless romanisation of Brahmic family, Indic scripts as employe ...
, which is contained in the
Mahabharata The ''Mahābhārata'' (; sa, महाभारतम्, ', ) is one of the two major of , the other being the '. It narrates the struggle between two groups of cousins in the and the fates of the and the princes and their successors ...

, which has 18 books. The
Kurukshetra War The Kurukshetra War ( sa, कुरुक्षेत्र युद्ध ), also called the Mahabharata War, is a war described in the Indian epic Indian epic poetry is the epic poetry written in the Indian subcontinent, traditionally ...

which the
epic Epic commonly refers to: * Epic poetry, a long narrative poem celebrating heroic deeds and events significant to a culture or nation * Epic film, a genre of film with heroic elements Epic or EPIC may also refer to: Arts, entertainment, and media ...
depicts, is between 18 armies (11 on the
Kuru Kuru may refer to: Anthropology and history * Kuru (disease) Kuru is a very rare, incurable and fatal neurodegenerative disorder Neurodegeneration is the progressive loss of structure or function of neurons A neuron or nerve cell is an ...
side, 7 on the
Pandava The Pandavas (Sanskrit Sanskrit (, attributively , ''saṃskṛta-'', nominalization, nominally , ''saṃskṛtam'') is a classical language of South Asia belonging to the Indo-Aryan languages, Indo-Aryan branch of the Indo-European langua ...
). The war itself lasts for 18 days. In the other Hindu epic, the
Ramayana ''Rāmāyana'' (; sa, रामायणम्, ) is one of the two major Sanskrit literature, Sanskrit Indian epic poetry, epics of ancient India and important text of Hinduism, the other being the ''Mahabharata, Mahābhārata''. The epi ...

, the war between
Rama Rama (; , ; ), Ram, Raman or Ramar, also known as Ramachandra (; , ), is a major deity in Hinduism Hinduism () is an and ', or way of life. It is the , with over 1.2 billion followers, or 15–16% of the global population, known a ...

and the demons also lasted 18 days. * In Babism the first 18 disciples of the
Báb The Báb, born Sayyed `Alí Muḥammad Shírází (; fa, سيد علی ‌محمد شیرازی; October 20, 1819 – July 9, 1850) was the founder of Bábism, and one of the central figures of the Baháʼí Faith. The Báb was a merchant fro ...
were known as the
Letters of the Living The Letters of the Living ( ar, حروف الحي) was a title provided by the Báb The Báb, born Sayyed `Alí Muḥammad Shírází (; fa, سيد علی ‌محمد شیرازی; October 20, 1819 – July 9, 1850) was the founder of Bábism ...
.

# As lucky or unlucky number

* In
Chinese tradition Chinese culture () is one of the world's oldest cultures, originating thousands of years ago. The culture prevails across a large geographical region in East Asia East Asia is the eastern region of Asia Asia () is Earth's larg ...
, 18 pronounced 十八 (shí bā) and is considered a lucky number due to similarity with 實發 (shì fā) 'definitely get rich', 'to get rich for sure'. *According to applications of numerology in Judaism, the letters of the word '' chai'' ("living") add up to 18. Thus, 18 is considered a lucky number and many gifts for B'nai Mitzvot and weddings are in \$18 increments.

# Age 18

In most countries, 18 is the
age of majority The age of majority is the threshold of adulthood as recognized or declared in law. It is the moment when minor Minor may refer to: * Minor (law), a person under the age of certain legal activities. ** A person who has not reached the age of ...

, in which a minor becomes a legal adult. It is also the
voting age A voting age is a minimum age established by law that a person must attain before they become eligible to vote in a public election. As of the present day, the most common voting age is 18 years; however, voting ages as low as 16 and as high as 2 ...

,
marriageable age Marriageable age (or marriage age) is the general age, as a legal ageLegal age or codified age refers to age at which a person may legally engage in a certain activity. Most frequently, this is the age of majority (also known as the "age of maturi ...
,
drinking age The legal drinking age is the minimum age at which a person can legally consume alcoholic beverage An alcoholic drink is a drink that contains ethanol, a type of alcohol produced by Ethanol fermentation, fermentation of grains, fruits, or othe ...
and
smoking age The smoking age is the minimum legal age required to purchase or use tobacco products. Most countries have laws that forbid sale of tobacco products to persons younger than certain ages, usually the age of majority. This article does not discuss ...

in most countries, though sometimes these ages are different than the age of majority. *In the United States, 18 is the: ** Age for sexual consent in eleven states and under federal law. **Minimum age to purchase firearms in thirty-eight states with the exception of handguns (21 under federal law). **
Marriageable age Marriageable age (or marriage age) is the general age, as a legal ageLegal age or codified age refers to age at which a person may legally engage in a certain activity. Most frequently, this is the age of majority (also known as the "age of maturi ...
without parental consent except for
Nebraska Nebraska () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

(19), Mississippi and Puerto Rico (21). **The minimum age at which one can purchase, rent, or buy tickets to
NC-17 The Motion Picture Association (MPA) film rating system is used in the United States and its territories to rate a film's suitability for certain audiences based on its content. The MPA rating system is a voluntary scheme that is not enforced by la ...

-rated films or buy video games with an AO rating.

# In sports

* In
association football Association football, more commonly known as simply football or soccer, is a team sport played with a sphere, spherical Ball (association football), ball between two teams of 11 football player, players. It is played by approximately 250&nbs ...
(soccer), "the 18" is a slang term for the
penalty area The penalty area or 18-yard box (also known less formally as the penalty box or simply box) is an area of an association football pitch A football pitch (also known as a football field or soccer field) is the playing surface for the game of a ...
. * In
Australian rules football Australian rules football, officially known as Australian football, or simply called "Aussie rules", "football" or "footy", is a contact sport played between two teams of 18 players on an Australian rules football playing field, oval field, o ...
(except in
AFL Women's AFL Women's (AFLW) is Australia's national semi-professional Australian rules football league for women's Australian rules football, female players. The 2017 AFL Women's season, first season of the league in February and March 2017 had 8 teams; t ...
), each team has 18 players on the field during play. * There are 18 holes on a regulation
golf Golf is a club-and-ball sport in which players use various Golf club, clubs to hit Golf ball, balls into a series of holes on a golf course, course in as few strokes as possible. Golf, unlike most ball games, cannot and does not utilize a sta ...

course. * In
Nippon Professional Baseball or NPB is the highest level of baseball in Japan Baseball Baseball is a bat-and-ball games, bat-and-ball game played between two opposing teams who take turns batting (baseball), batting and fielding. The game proceeds when a pl ...
(Japanese baseball), No.18 is known as
Ace An ace is a playing card A playing card is a piece of specially prepared , heavy paper, thin cardboard, , cotton-paper blend, or thin plastic that is marked with distinguishing motifs. Often the front (face) and back of each card has a to ...
number.

# In other fields

Eighteen is also: * A 2005 movie directed by Richard Bell and starring
Brendan Fletcher Brendan Fletcher (born December 15, 1981) is a Canadian actor, screenwriter A screenplay writer (also called screenwriter for short), scriptwriter or scenarist, is a writer who practices the craft of screenwriting, writing screenplays on w ...
and
Alan Cumming Alan Cumming (born 27 January 1965) is a Scottish-American actor, singer, writer, filmmaker, and activist who has acted in numerous films, television shows, and plays. His London stage appearances include ''Hamlet ''The Tragedy of Hamle ...

. * A 2002 album by electronic artist
Moby Richard Melville Hall (born September 11, 1965), known professionally as Moby, is an American musician, songwriter, singer, producer, and animal rights activist. He has sold 20 million records worldwide. AllMusic AllMusic (previously known ...

. * The number of chapters into which
James Joyce James Augustine Aloysius Joyce (2 February 1882 – 13 January 1941) was an Irish novelist, short story writer, poet and literary critic. He contributed to the modernist , Solomon Guggenheim Museum 1946–1959 Modernism is both a philosophy ...
's epic novel ''
Ulysses Ulysses is the Roman name for Odysseus, a hero in ancient Greek literature. Ulysses may also refer to: People * Ulysses (given name), including a list of people with this name Places in the United States * Ulysses, Kansas * Ulysses, Kentucky * U ...
'' is divided. * Russ Wheeler's car number in the film ''
Days of Thunder ''Days of Thunder'' is a 1990 American sports Sport pertains to any form of competitive Competition arises whenever two or more parties strive for a common goal A goal is an idea of the future or desired result that a person or ...
''. * The number of wheels on the most common type of North American
tractor-trailer A semi-tractor-trailer truck, also known as simply a semi-trailer truck, semi-tractor truck, semi-tractor-trailer or tractor-trailer truck, is the combination of a tractor unit A tractor unit (also known as a truck unit, prime mover, te ...
truck, which are hence often called ''18-wheelers''. * The number of the French department
Cher Cher (; born Cherilyn Sarkisian; May 20, 1946) is an American singer, actress and television personality. Often referred to by the media as the "Goddess of Pop", she has been described as embodying female autonomy in a male-dominated industry ...
and the Turkish province
Bitlis Bitlis ( hy, Բաղեշ '; ku, Bidlîs; ota, بتليس) is a city in eastern Turkey and the capital of Bitlis Province Bitlis Province ( tr, , ku, Parêzgeha Bidlîsê) is a province of eastern Turkey Turkey ( tr, Türkiye ), official ...
. *
DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital Digital usually refers to something using digits, particularly binary digits. Technology and computing Hardware *Digital electronics Digital electr ...

-18 is double-sided, double-layered DVD format. * A Canon error message, see
E18 error The E18 error as it appears on a camera's LCD display (an Ixus II in this example). The E18 error is an error message An error message is information displayed when an unforeseen problem occurs, usually on a computer A computer is a machin ...
. *
Android 18 , born as , is a fictional character In fiction Fiction generally is a narrative form, in any media (communication), medium, consisting of people, events, or places that are imagination, imaginary—in other words, not based strictly on histo ...
, a fictional character in the ''
Dragon Ball is a Japanese media franchise A media franchise, also known as a multimedia franchise, is a collection of related media Media may refer to: Physical means Communication * Media (communication), tools used to deliver information o ...

'' manga and anime series. *
18th Street gang 18th Street, also known as , , , or simply in Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas The Americas (also collectively called America) is a landmass comprising th ...
, a Hispanic American gang. * The Hindu epic
Mahabharata The ''Mahābhārata'' (; sa, महाभारतम्, ', ) is one of the two major of , the other being the '. It narrates the struggle between two groups of cousins in the and the fates of the and the princes and their successors ...

has eighteen sections, involves eighteen armies and is about a war fought over eighteen days. * In the Chinese mythos,
Hell In religion Religion is a - of designated and practices, , s, s, , , , , or , that relates humanity to , , and elements; however, there is no scholarly consensus over what precisely constitutes a religion. Different religions may o ...

has 18 levels. * In Chinese folklore, the
Shaolin temple The Shaolin Monastery (), also known as the Shaolin Temple, is a Chan ("Zen") Buddhist temple located in Dengfeng County, Henan Province Henan (; alternatively Honan) is a landlocked province of China, in the central part of the cou ...
had a group of 18 bronze Monks. Initiates could only be considered full graduates of Shaolin
martial art Martial arts are codified systems and traditions of combat practiced for a number of reasons such as self-defense; military and law enforcement applications; combat sport, competition; physical, mental, and spiritual development; entertainment; and ...

s if they could defeat them in combat. * In
Neo-Nazi Neo-Nazism refers to the post–World War II militant, social, and political movements seeking to revive and reinstate Nazism, Nazi ideology. Neo-Nazis seek to employ their ideology to promote hatred and white supremacy, attack racial and e ...
circles 18 is the numerical sign for
Adolf Hitler Adolf Hitler (; 20 April 188930 April 1945) was an Austrian-born German politician who was the dictator of Nazi Germany, Germany from 1933 to 1945. Adolf Hitler's rise to power, He rose to power as the leader of the Nazi Party, becoming Cha ...

(1 standing for A and 8 standing for H). It is also the number for the -based terrorist group
Combat 18 Combat 18 (C18 or 318) is a neo-Nazi Neo-Nazism refers to the post–World War II militant, social, and political movements seeking to revive and reinstate Nazism, Nazi ideology. Neo-Nazis seek to employ their ideology to promote hatre ...
. * In 1990
Megadeth Megadeth is an American heavy metal music, heavy metal band formed in Los Angeles in 1983 by vocalist/guitarist Dave Mustaine and bassist David Ellefson. Known for their technically complex guitar work and musicianship, Megadeth is one of the " ...
released " Hangar 18" as a single from ''
Rust in Peace ''Rust in Peace'' is the fourth studio album by American heavy metal band Megadeth, released on September 24, 1990 by Capitol Records Capitol Records (legal name: Capitol Records, LLC, until 2007 Capitol Records Inc.) is an American record l ...

''. *
Eighteen Visions Eighteen Visions is an American metalcore band from Orange County, California, formed in October 1995. The band broke up in April 2007, less than a year after their major label debut was released through Epic Records, Epic and Trustkill Records. ...
(often abbreviated to 18V), an
alternative metal Alternative metal (also known as alt-metal) is a rock music fusion genre that infuses heavy metal music, heavy metal with influences from alternative rock and other genres not normally associated with metal. Alternative metal bands are often ch ...
/
metalcore Metalcore (or metallic hardcore) is a :Fusion music genres, fusion music genre that combines elements of extreme metal and hardcore punk. As with other styles blending metal and hardcore, such as crust punk and grindcore, metalcore is noted for it ...
band from
Orange County, California Orange County is located in the Los Angeles metropolitan area Greater Los Angeles, with a 2019 population of 18,710,563, is the second-largest urban region area in the United States The United States of America (U.S.A. or USA) ...
. * Eighteen Eighteen, a
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. With over 60 million people, it is the world's 23rd-most populous nation and covers an area of . South Africa has three capital citie ...

n
Rap artist Rapping (also rhyming, spitting, emceeing or MCing) is a musical form of vocal delivery that incorporates "rhyme, rhythmic speech, and street vernacular", which is performed or chanted in a variety of ways, usually over a backing beat or musi ...
. * "
I'm Eighteen "I'm Eighteen" is a song by rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, ch ...
",
Alice Cooper Alice Cooper (born Vincent Damon Furnier, February 4, 1948) is an American singer, songwriter, and actor whose career spans over 50 years. With a raspy voice and a stage show that features numerous props, including pyrotechnics, guillotines, e ...

's first Top Ten hit single, from their 1971 album ''
Love It to Death ''Love It to Death'' is the third studio album by American rock group Alice Cooper Alice Cooper (born Vincent Damon Furnier, February 4, 1948) is an American singer, songwriter, and actor whose career spans over 50 years. With a raspy voice ...
''. * A surname, recorded in East Anglia in the 18th century. * In English speech, commonly confused with the number , as they sound similar when spoken * Some of semi-trucks have 18 wheel (10 in the tractor & 8 in the trailer)