18 (number)

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18 10 8

18 (eighteen) is the natural number following 17 and preceding 19.

Cardinal 18
eighteen
Ordinal 18th
eighteenth
Factorization 2 \cdot 3^2
Divisors 1, 2, 3, 6, 9, 18
Roman numeral XVIII
Roman numeral (Unicode) XVIII, xviii
Binary 10010
Octal 22
Duodecimal 16
Hexadecimal 12
Look up eighteen in
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Contents

[edit] In mathematics

Eighteen is a composite number, its proper divisors 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.

It is a heptagonal number, and as the sum of the first three pentagonal numbers, it is a pentagonal pyramidal number. It is also the sum of the totient function for the first seven integers.

In base 10 it is a Harshad number.

[edit] In science

[edit] Astronomy

[edit] In religion and literature

  • The Hebrew word for "life" is חי (chai), which has a numerical value 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.
  • Joseph Heller's novel Catch-22 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.[1]

[edit] As lucky or unlucky number

  • In Chinese tradition, the number 18, normally 十八 (shí bā), 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[citation needed]

It is also considered a number of the devil for many reasons. 6+6+6=18 666 is the number of the devil. In chapter 13 of the book of revelations it is in the verse 18 in which the book talks about the number 666. There are also 18 letters in the words six-hundred sixty six.

[edit] Age 18

In many parts of the world, 18 is the age minimum for purchasing tobacco and alcoholic beverages. It is also the voting age in many countries. During the Vietnam War, Americans could be drafted at an age as low as 18, but were not allowed to vote in most states until they were 21. A movement spread to lower the voting age, and in 1971, the Twenty-sixth Amendment extended a guarantee of suffrage to anyone 18 years or older in all states. The voting age was lowered from 21 to 18 in the U.K. and many other nations around that time.

Eighteen is also the age in most countries at which a person may appear in a pornographic video, if pornography is legal at all, or express legal consent to sexual relations with another.

An eighteen year-old is able to purchase goods from television commercials which otherwise would have been a liability issue for the seller.

In addition, eighteen year-olds in the United States have the right to bear arms, own property, marry without parental consent, get an abortion, donate their body to science, obtain a passport, and serve on a jury. With these new privileges come responsibility: eighteen year-olds are tried as adults in court. However, there are exceptions to this tradeoff: minors can be tried as adults as early as 16[citation needed] or sometimes even 7[citation needed] years of age, and minors can be emancipated as early as 16[citation needed] years of age, putting older minors at somewhat of a disparity of lacking the protections of children and the advantages of an adult, yet being disadvantaged by being held to the same level of responsibility or accountability as an adult.[verification needed]

In many countries 18 is the age of majority.

See also: 18 certificate, Coming of age

[edit] In music

[edit] In other fields

Eighteen is also:

  • Bobby Labonte's car number in the NASCAR Winston Cup Series when he won the 2000 Championship. This is J. J. Yeley's car number as of 2006.
  • The number of holes in a stipulated round of golf
  • The number of chapters into which James Joyce's epic novel Ulysses is divided
  • A slang term used in Soccer for the Penalty Area
  • The number of wheels on the most common type of tractor-trailer truck, which are hence often called 18-wheelers
  • The customary percentage to tip a waitress in a restaurant by groups of four or more
  • The number of the French department Cher and the Turkish province Bitlis
  • DVD-18 is double-sided, double-layered DVD format
  • A Canon error message, see E18 error
  • In neo-Nazi circles, a code word for Adolf Hitler. The number comes from the position of the letters in the alphabet: A = 1, H = 8. See also 88
  • Dragon Ball Z Character, Android 18.
  • Jersey number of football players Peyton Manning and Randy Moss.
  • Jersey number of former basketball player Phil Jackson
  • Uniform number of former baseball player Don Larsen. The number shows prominently in a photograph taken just before the last pitch he made in his perfect game in the 1956 World Series. (When this picture was printed in Baseball's Unforgettable Games by Joseph Reichler and Ben Olan in 1960, they gave it the caption "The Writing on the Wall.")
  • The Hindu epic Mahabharata has eighteen sections, involves eighteen armies and is about a war fought over eighteen days
  • The sacred literature of the Hindus known as Bhagavad Gita has eighteen chapters.

[edit] Historical years

A.D. 18, 18 B.C., 1918, 2018, etc.

[edit] See also

[edit] Notes

  1. ^ 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, 1996
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