18 (number)
Encyclopedia
18 is the natural number
following 17
and preceding 19
.
In speech, the numbers 18 and 80 are sometimes confused. When carefully enunciated, they differ in which syllable is stressed
: 18 eɪtˈtiːn vs 80 ˈeɪti. However, in dates such as 1864, or when contrasting numbers in the teens, such as 17, 18, 19, the stress shifts to the first syllable: 18 ˈeɪttiːn. In some dialects, such as General American
, there is little confusion because the single t sound in 80 becomes a d-like flap [ɾ], whereas the double t sound in 18 does not.
, its proper divisor
s being 1, 2, 3, 6 and 9. Three of these divisors (3, 6 and 9) add up to 18, hence 18 is a semiperfect number
. Eighteen is the first inverted square-prime of the form p.q2.
It is a heptagonal number, and as the sum of the first three pentagonal number
s, it is a pentagonal pyramidal number
. It is also the sum of the totient function for the first seven integers.
Eighteen is the second abundant number with the aliquot sum of 21 (117% in abundance) in the aliquot sequence
(18, 21
, 11
, 1, 0) thus being the first composite number
in the 11-aliquot tree. Eighteen is the aliquot sum of only one number the square 289.
In base 10 it is a Harshad number
.
18, aside from 0, is the only number that equals twice the sum of its decimal digits.
.
In most countries 18 is the voting age.
In many countries 18 is the age of sexual consent
.
18 is the age when a person can watch an NC-17 movie.
Natural number
In mathematics, the natural numbers are the ordinary whole numbers used for counting and ordering . These purposes are related to the linguistic notions of cardinal and ordinal numbers, respectively...
following 17
17 (number)
17 is the natural number following 16 and preceding 18. It is prime.In spoken English, the numbers 17 and 70 are sometimes confused because they sound similar. When carefully enunciated, they differ in which syllable is stressed: 17 vs 70...
and preceding 19
19 (number)
19 is the natural number following 18 and preceding 20. It is a prime number.In English speech, the numbers 19 and 90 are often confused. When carefully enunciated, they differ in which syllable is stressed: 19 vs 90...
.
In speech, the numbers 18 and 80 are sometimes confused. When carefully enunciated, they differ in which syllable is stressed
Stress (linguistics)
In linguistics, stress is the relative emphasis that may be given to certain syllables in a word, or to certain words in a phrase or sentence. The term is also used for similar patterns of phonetic prominence inside syllables. The word accent is sometimes also used with this sense.The stress placed...
: 18 eɪtˈtiːn vs 80 ˈeɪti. However, in dates such as 1864, or when contrasting numbers in the teens, such as 17, 18, 19, the stress shifts to the first syllable: 18 ˈeɪttiːn. In some dialects, such as General American
General American
General American , also known as Standard American English , is a major accent of American English. The accent is not restricted to the United States...
, there is little confusion because the single t sound in 80 becomes a d-like flap [ɾ], whereas the double t sound in 18 does not.
In mathematics
Eighteen is a composite numberComposite number
A composite number is a positive integer which has a positive divisor other than one or itself. In other words a composite number is any positive integer greater than one that is not a prime number....
, its proper divisor
Divisor
In mathematics, a divisor of an integer n, also called a factor of n, is an integer which divides n without leaving a remainder.-Explanation:...
s being 1, 2, 3, 6 and 9. Three of these divisors (3, 6 and 9) add up to 18, hence 18 is a semiperfect number
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....
. Eighteen is the first inverted square-prime of the form p.q2.
It is a heptagonal number, and as the sum of the first three pentagonal number
Pentagonal number
A pentagonal number is a figurate number that extends the concept of triangular and square numbers to the pentagon, but, unlike the first two, the patterns involved in the construction of pentagonal numbers are not rotationally symmetrical...
s, it is a pentagonal pyramidal number
Pentagonal pyramidal number
A pentagonal pyramidal number is a figurate number that represents the number of objects in a pyramid with a pentagonal base. The nth pentagonal pyramidal number is equal to the sum of the first n pentagonal numbers....
. It is also the sum of the totient function for the first seven integers.
Eighteen is the second abundant number with the aliquot sum of 21 (117% in abundance) in the aliquot sequence
Aliquot sequence
In mathematics, an aliquot sequence is a recursive sequence in which each term is the sum of the proper divisors of the previous term. The aliquot sequence starting with a positive integer k can be defined formally in terms of the sum-of-divisors function σ1 in the following way:For example, the...
(18, 21
21 (number)
21 is the natural number following 20 and preceding 22.-In mathematics:Twenty-one is the fifth discrete Semiprime and the second in the family. With 22 it forms the second discrete Semiprime pair...
, 11
11 (number)
11 is the natural number following 10 and preceding 12.Eleven is the first number which cannot be counted with a human's eight fingers and two thumbs additively. In English, it is the smallest positive integer requiring three syllables and the largest prime number with a single-morpheme name...
, 1, 0) thus being the first composite number
Composite number
A composite number is a positive integer which has a positive divisor other than one or itself. In other words a composite number is any positive integer greater than one that is not a prime number....
in the 11-aliquot tree. Eighteen is the aliquot sum of only one number the square 289.
In base 10 it is a Harshad number
Harshad number
A Harshad number, or Niven number in a given number base, is an integer that is divisible by the sum of its digits when written in that base. Harshad numbers were defined by D. R. Kaprekar, a mathematician from India. The word "Harshad" comes from the Sanskrit + , meaning joy-giver. The Niven...
.
18, aside from 0, is the only number that equals twice the sum of its decimal digits.
In science
- The atomic numberAtomic numberIn chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
of argonArgonArgon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide... - The 18-electron rule18-Electron ruleThe 18-electron rule is a rule of thumb used primarily for predicting formulas for stable metal complexes. The rule rests on the fact that valence shells of a transition metal consists of nine valence orbitals, which collectively can accommodate 18 electrons either as nonbinding electron pairs or...
is a rule of thumbRule of thumbA rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination...
in transition metalTransition metalThe term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
chemistryChemistryChemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
for characterising and predicting the stability of metal complexes - The number of years in the Saros cycleSaros cycleThe saros is a period of 223 synodic months , that can be used to predict eclipses of the Sun and Moon. One saros after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle...
of eclipsesEclipse cycleEclipses may occur repeatedly, separated by certain intervals of time: these intervals are called eclipse cycles. The series of eclipses separated by a repeat of one of these intervals is called an eclipse series.- Eclipse conditions :...
of the sun and moon
In religion and literature
- The HebrewHebrew languageHebrew is a Semitic language of the Afroasiatic language family. Culturally, is it considered by Jews and other religious groups as the language of the Jewish people, though other Jewish languages had originated among diaspora Jews, and the Hebrew language is also used by non-Jewish groups, such...
word for "life" is חי (chaiChai (symbol)Chai is a symbol and word that figures prominently in Jewish culture. It consists of the letters of the Hebrew alphabet Chet and Yod .The Hebrew word "living" is related to the term for "life", chaim; ḥayyim....
), which has a numerical valueGematriaGematria or gimatria is a system of assigning numerical value to a word or phrase, in the belief that words or phrases with identical numerical values bear some relation to each other, or bear some relation to the number itself as it may apply to a person's age, the calendar year, or the like...
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 JudaismJudaismJudaism ) is the "religion, philosophy, and way of life" of the Jewish people...
, in the TalmudTalmudThe Talmud is a central text of mainstream Judaism. It takes the form of a record of rabbinic discussions pertaining to Jewish law, ethics, philosophy, customs and history....
; Pirkei Avot (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 (marriage canopy)). (See Coming of ageComing of ageComing of age is a young person's transition from childhood to adulthood. The age at which this transition takes place varies in society, as does the nature of the transition. It can be a simple legal convention or can be part of a ritual, as practiced by many societies...
, Age of majorityAge of majorityThe age of majority is the threshold of adulthood as it is conceptualized in law. It is the chronological moment when minors cease to legally be considered children and assume control over their persons, actions, and decisions, thereby terminating the legal control and legal responsibilities of...
). - In Ancient Roman custom the number 18 can symbolise a blood relative.
- Joseph HellerJoseph HellerJoseph Heller was a US satirical novelist, short story writer, and playwright. His best known work is Catch-22, a novel about US servicemen during World War II...
's novel Catch-22Catch-22Catch-22 is a satirical, historical novel by the American author Joseph Heller. He began writing it in 1953, and the novel was first published in 1961. It is set during World War II in 1943 and is frequently cited as one of the great literary works of the twentieth century...
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 18Mila 18Mila 18 is a novel by Leon Uris set in German-occupied Warsaw, Poland before and during World War II. Leon Uris's work, based on real events, covers the Nazi occupation of Poland and the atrocities of systematically dehumanising and eliminating the Jewish People of Poland...
. - There are 18 chapters in the Bhagavad GitaBhagavad GitaThe ' , also more simply known as Gita, is a 700-verse Hindu scripture that is part of the ancient Sanskrit epic, the Mahabharata, but is frequently treated as a freestanding text, and in particular, as an Upanishad in its own right, one of the several books that constitute general Vedic tradition...
, which is contained in the MahabharataMahabharataThe Mahabharata is one of the two major Sanskrit epics of ancient India and Nepal, the other being the Ramayana. The epic is part of itihasa....
, which has 18 books. The Kurukshetra WarKurukshetra warAccording to the Indian epic poem Mahābhārata, a dynastic succession struggle between two groups of cousins of an Indo-Aryan kingdom called Kuru, the Kauravas and Pandavas, for the throne of Hastinapura resulted in the Kurukshetra War in which a number of ancient kingdoms participated as allies of...
which the epicIndian epic poetryIndian epic poetry is the epic poetry written in the Indian subcontinent, traditionally called Kavya . The Ramayana and Mahabharata, originally composed in Sanskrit and translated thereafter into many other Indian languages, are some of the oldest surviving epic poems on earth and form part of...
depicts, is between 18 armies (11 on the Kuru side, 7 on the PandavaPandavaIn the Hindu epic Mahābhārata, the Pandava are the five acknowledged sons of Pandu , by his two wives Kunti and Madri. Their names are Yudhisthira, Bhima, Arjuna, Nakula and Sahadeva. Although, Karna is told by Lord Krishna that according to the laws and ethics he is the first son of Kunti making...
). - A shape looking like 18 in Arabic numbersEastern Arabic numeralsThe Eastern Arabic numerals are the symbols used to represent the Hindu-Arabic numeral system in conjunction with the Arabic alphabet in the countries of the Arab world....
is formed by the lines on the palm of the right hand.
As lucky or unlucky number
- In Chinese tradition, the number 18 is normally 十八 (shí bā), but it can also be read as 幺八 (yāo bā), which sounds like 要发 (yào fā), meaning that one is going to prosper. Thus, building floors numbered "18" are often very expensive in China. Contrastingly, though, the floor 18 of a building in Northern China is viewed as a floor to be avoided, as one can never return from the 18th level of hell.
Age 18
In most countries 18 is the age of majorityAge of majority
The age of majority is the threshold of adulthood as it is conceptualized in law. It is the chronological moment when minors cease to legally be considered children and assume control over their persons, actions, and decisions, thereby terminating the legal control and legal responsibilities of...
.
In most countries 18 is the voting age.
In many countries 18 is the age of sexual consent
Age of consent
While the phrase age of consent typically does not appear in legal statutes, when used in relation to sexual activity, the age of consent is the minimum age at which a person is considered to be legally competent to consent to sexual acts. The European Union calls it the legal age for sexual...
.
18 is the age when a person can watch an NC-17 movie.
In other fields
Eighteen is also:- 18:00, a time on the 24-hour clock24-hour clockThe 24-hour clock is a convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23. This system is the most commonly used time notation in the world today...
corresponding to 6:00 PM12-hour clockThe 12-hour clock is a time conversion convention in which the 24 hours of the day are divided into two periods called ante meridiem and post meridiem...
. - A 2005 movie directed by Richard Bell and starring Brendan FletcherBrendan FletcherBrendan Fletcher is a Canadian actor.-Life and career:Fletcher was born in Comox Valley, British Columbia and went to junior high school at Lake Trail in Courtenay, British Columbia....
and Alan CummingAlan CummingAlan Cumming, OBE is a Scottish stage, television and film actor, singer, writer, director, producer and author. His roles have included the Emcee in Cabaret, Boris Grishenko in GoldenEye, Kurt Wagner/Nightcrawler in X2: X-Men United, Mr. Elton in Emma, and Fegan Floop in the Spy Kids trilogy...
. - Bobby LabonteBobby LabonteRobert Alan "Bobby" Labonte is an American race car driver in the NASCAR Sprint Cup Series. He currently drives the #47 Kroger/Clorox/Kimberly-Clark/Kingsford/Reese Towpower Hitches Toyota Camry for JTG Daugherty Racing. He currently resides in Trinity, North Carolina. He is married to his wife...
's car number in the NASCAR Winston CupNEXTEL CupThe NASCAR Sprint Cup Series is the top racing series of the National Association for Stock Car Auto Racing . The series was originally known as the Strictly Stock Series and Grand National Series . While leasing its naming rights to R. J...
Series when he won the 20002000 in NASCARThe 2000 NASCAR Winston Cup Season began on Sunday February 13 and ended on Sunday November 20. Joe Gibbs Racing driver Bobby Labonte was crowned champion at season's end. The NASCAR Manufacturers' Championship was won by Ford when they captured 14 wins and 234 points to better Pontiac's 11 wins...
Championship. This is J. J. YeleyJ. J. YeleyChristopher Beltram Hernandez Yeley is a NASCAR driver. Nicknamed "J. J." , he is currently a competitor in the NASCAR Sprint Cup Series, driving for Front Row Motorsports.-Open wheel:Yeley initially made a mark for himself in the world of auto racing when he took the Hoosier state by...
's car number until the end of the 2007 Nextel Cup Season2007 in NASCARThe 2007 NASCAR NEXTEL Cup season began on February 10, 2007 at Daytona International Speedway with the Budweiser Shootout and ended on November 18 of that same year at Homestead-Miami Speedway with the Ford 400. The Chase for the NEXTEL Cup began with the Sylvania 300 at New Hampshire...
. Kyle BuschKyle BuschKyle Thomas Busch, is an American NASCAR driver and team owner. He currently drives the No. 18 Mars/Interstate Batteries Toyota Camry for Joe Gibbs Racing in the Sprint Cup Series, the No. 18 Z-Line Designs/NOS Energy Drink Toyota Camry for Joe Gibbs in the Nationwide Series, and the No...
took the car number in 20082008 in NASCARThere were three NASCAR national series in 2008:*2008 NASCAR Sprint Cup Series - The top racing series in NASCAR*2008 NASCAR Nationwide Series - The second-tier NASCAR racing series*2008 NASCAR Craftsman Truck Series - The third-tier NASCAR racing series...
. - A 2002 album by electronic artist MobyMobyRichard Melville Hall , better known by his stage name Moby, is an American musician, DJ, and photographer. He is known mainly for his sample-based electronic music and his outspoken liberal political views, including his support of veganism and animal rights.Moby gained attention in the early...
. - The number of holes in a stipulated round of golfGolfGolf is a precision club and ball sport, in which competing players use many types of clubs to hit balls into a series of holes on a golf course using the fewest number of strokes....
- The number of chapters into which James JoyceJames JoyceJames Augustine Aloysius Joyce was an Irish novelist and poet, considered to be one of the most influential writers in the modernist avant-garde of the early 20th century...
's epic novel UlyssesUlysses (novel)Ulysses is a novel by the Irish author James Joyce. It was first serialised in parts in the American journal The Little Review from March 1918 to December 1920, and then published in its entirety by Sylvia Beach on 2 February 1922, in Paris. One of the most important works of Modernist literature,...
is divided - Russ Wheeler's car number in the film Days of ThunderDays of ThunderDays of Thunder is a 1990 American auto racing film released by Paramount Pictures, produced by Don Simpson and Jerry Bruckheimer and directed by Tony Scott. The cast includes Tom Cruise, Nicole Kidman, Robert Duvall, Randy Quaid, Cary Elwes and Michael Rooker. The film also features appearances...
- A slang term used in association football for the Penalty AreaPenalty areaThe penalty area , is an area of an association football pitch. It is rectangular and extends to each side of the goal and in front of it. Within the penalty area is the penalty spot , which is from the goal line, directly in-line with the centre of the goal...
- The number of wheels on the most common type of North American tractor-trailer truck, which are hence often called 18-wheelers
- The number of the French department Cher and the Turkish provinceProvinces of TurkeyTurkey is divided into 81 provinces, called il in Turkish .A province is administered by an appointed governor , and was formerly termed a "governorate" ....
BitlisBitlisBitlis is a town in eastern Turkey and the capital of Bitlis Province. The town is located at an elevation of 1,400 metres, 15 km from Lake Van, in the steep-sided valley of the Bitlis River, a tributary of the Tigris. The local economy is mainly based on agricultural products which include... - DVDDVDA DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
-18 is double-sided, double-layered DVD format - A Canon error message, see E18 errorE18 errorThe E18 error is an error message on Canon digital cameras. The E18 error occurs when anything prevents the zoom lens from properly extending or retracting...
- In neo-Nazi circles, a code wordCode wordIn communication, a code word is an element of a standardized code or protocol. Each code word is assembled in accordance with the specific rules of the code and assigned a unique meaning...
for Adolf HitlerAdolf HitlerAdolf Hitler was an Austrian-born German politician and the leader of the National Socialist German Workers Party , commonly referred to as the Nazi Party). He was Chancellor of Germany from 1933 to 1945, and head of state from 1934 to 1945...
. The number comes from the position of the letters in the alphabet: AAA is the first letter and a vowel in the basic modern Latin alphabet. It is similar to the Ancient Greek letter Alpha, from which it derives.- Origins :...
= 1, HHH .) is the eighth letter in the basic modern Latin alphabet.-History:The Semitic letter ⟨ח⟩ most likely represented the voiceless pharyngeal fricative . The form of the letter probably stood for a fence or posts....
= 8. See also 8888 (number)88 is the natural number following 87 and preceding 89.- In mathematics :Eighty-Eight is a refactorable number, a primitive semiperfect number and an untouchable number... - Android 18, a fictional character in the metaseries Dragon Ball.
- 18th Street gang18th Street gang18th Street gang is considered to be the largest transnational criminal gang in Los Angeles, California. It is estimated that there are thousands of members in Los Angeles County alone...
, a Hispanic American gang - The Hindu epic MahabharataMahabharataThe Mahabharata is one of the two major Sanskrit epics of ancient India and Nepal, the other being the Ramayana. The epic is part of itihasa....
has eighteen sections, involves eighteen armies and is about a war fought over eighteen days - In some countries the number 18 means blood (relative)
- In the Chinese mythos, HellHellIn many religious traditions, a hell is a place of suffering and punishment in the afterlife. Religions with a linear divine history often depict hells as endless. Religions with a cyclic history often depict a hell as an intermediary period between incarnations...
has 18 levels - In Chinese folklore, the Shaolin temple had a group of 18 bronze Monks. Initiates could only be considered full graduates of Shaolin martial arts if they could defeat them in combat.
- In 1990 MegadethMegadethMegadeth is an American heavy metal band from Los Angeles, California which was formed in 1983 by guitarist/vocalist Dave Mustaine, bassist Dave Ellefson and guitarist Greg Handevidt, following Mustaine's expulsion from Metallica. The band has since released 13 studio albums, three live albums, two...
released Hanger 18 as a single for the Rust in Piece Album. - Eighteen VisionsEighteen VisionsEighteen Visions was an American metalcore band from Orange County, California, United States. Formed in October of 1995, the group was one of the first practitioners involved in the metalcore genre...
(often abbreviated to 18V), an alternative metalAlternative metalAlternative metal is a genre of alternative rock and heavy metal that gained popularity in the early 1990s. Most notably, alternative metal bands are characterized by heavy guitar riffs and experimental approaches to heavy music.-Origins:...
/metalcoreMetalcoreMetalcore is a subgenre of heavy metal combining various elements of extreme metal and hardcore punk. The name is a portmanteau of the names of the two genres. The term took on its current meaning in the mid-1990s, describing bands such as Earth Crisis, Deadguy and Integrity...
band from Orange County, CaliforniaOrange County, CaliforniaOrange County is a county in the U.S. state of California. Its county seat is Santa Ana. As of the 2010 census, its population was 3,010,232, up from 2,846,293 at the 2000 census, making it the third most populous county in California, behind Los Angeles County and San Diego County...
. - Eighteen Eighteen, a South AfricaSouth AfricaThe Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
n Rap artist. - "I'm EighteenI'm Eighteen"I'm Eighteen" is a 1970 song by rock band Alice Cooper, featured on their first major label release album Love It to Death. It was released in November 1970, 3 months prior to the album, and became the band's breakthrough hit.-Achievements:...
", Alice CooperAlice CooperAlice Cooper is an American rock singer, songwriter and musician whose career spans more than four decades...
's first Top Ten hit single, from their 1971 album Love It to DeathLove It to DeathRolling Stones John Mendelsohn found it favorable. He explained that it "represents at least a modest oasis in the desert of dreary blue-jeaned aloofness served up in concert by most American rock-and-rollers." However, referring to "Black Juju" he also stated that "the one bummer on this album is...
. - Eighteen is also a surname, recorded in East Anglia in the 18th century