19 (number)

19 (nineteen) is the natural number following 18 and preceding 20. It is a prime number.

"XIX" redirects here. For other uses, see 19 (disambiguation).

← 18 19 20 →
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Cardinalnineteen
Ordinal19th
(nineteenth)
Numeral systemnonadecimal
Factorizationprime
Prime8th
Divisors1, 19
Greek numeralΙΘ´
Roman numeralXIX
Binary100112
Ternary2013
Octal238
Duodecimal1712
Hexadecimal1316

Mathematics
19 is a centered triangular number

19 is the 8th prime number, the seventh Mersenne prime exponent,[1] and the second base-10 repunit prime exponent.[2] 19 is the maximum number of fourth powers needed to sum up to any natural number, and in the context of Waring's problem, 19 is the fourth value of g(k). In addition, 19 is a Heegner number[3] and a centered hexagonal number.[4] 19 is also a centered triangular number,[5] being the smallest such number that is also prime. Moreover, there exists only one nontrivial normal magic hexagon: the one composed of 19 cells.

Science

Religion

Islam
  • The number of angels guarding Hell ("Hellfire") ("Saqar") according to the Qur'an: "Over it are nineteen" (74:30), after which the Qur'an describes this number as being "a trial for those who disbelieve" (74:31), a sign for people of the scripture to be "convinced" (74:31) and that believers "will increase in faith" (74:31) due to it...
  • The Number of Verse and Sura together in the Qur'an which announces Jesus son of Maryam's (Mary's) birth (Qur'an 19:19).
  • A group called United Submitter International claim the Quran has mathematical structure based on the number 19. The gematrical value of WAHD = 6+1+8+4=19, Wahd means 'One' (God) to the first verse (1:1), known as Bas-malah, consists of 19 Arabic letters or the Quran consists of 114 (19x6) su-ras etc.

Baháʼí faith

In the Bábí and Baháʼí Faiths, a group of 19 is called a Váhid, a Unity (Arabic: واحد wāhid, "one"). The numerical value of this word in the Abjad numeral system is 19.

Music
  • "19" is a 1985 song by Paul Hardcastle, including sampled soundbites taken from a documentary about the Vietnam War in which 19 is claimed to have been the average age of United States soldiers killed in the conflict.[6] The song was parodied by British satirist Rory Bremner under the pseudonym 'The Commentators,' as N-n-nineteen, Not Out, the title referring to the batting average of David Gower, the England cricket captain, during his side's risible performance against the West Indies in 1984 when they lost 5–0.
  • "I Was Only Nineteen" by the Australian group Redgum reached number one on the Australian charts in 1983. In 2005 a hip hop version of the song was produced by The Herd.
  • 19 is the name of Adele's 2008 debut album, so named since she was 19 years old at the time.
  • "Hey Nineteen" is a song by American jazz rock band Steely Dan, on the 1980 album Gaucho.
  • Nineteen has been used as an alternative to twelve for a division of the octave into equal parts. This idea goes back to Salinas in the sixteenth century, and is interesting in part because it gives a system of meantone tuning, being close to 1/3 comma meantone. See 19 equal temperament.
  • Some organs use the 19th harmonic to approximate a minor third.

Literature

Games
A 19x19 Go board
  • The game of Go is played on a grid of 19×19 lines (though variants can be played on grids of other sizes).
  • Though the maximum score for a cribbage hand is 29, there is no combination of cards that adds up to 19 points. Many cribbage players, therefore, jokingly refer to a zero-point hand as "a 19 hand."
  • In Ecuadorian card game "40", when counting the number of cards gathered in a hand, the limit is 19, after which the count starts at 6 and represents the points achieved during that hand.

Age 19
  • This is the age of majority in some countries, Canadian provinces, and U.S. states.
  • This is the minimum age that is legal to buy tobacco products in the states Alabama, Alaska, Utah and several counties in New York including Nassau, and Onondaga.[7]
  • This is the minimum age at which one can drink and buy alcohol in Canada except for the provinces of Alberta, Manitoba, and Quebec where the drinking and purchase age of alcohol is 18.

In sports
  • In golf, the '19th hole' is the clubhouse bar and in match play, if there is a tie after 18 holes, an extra hole(s) is played. In miniature golf it is an extra hole on which the winner earns an instant prize.

Other fields

References
  1. "Sloane's A000043 : Mersenne exponents". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  2. Guy, Richard; Unsolved Problems in Number Theory, p. 7 ISBN 1475717385
  3. "Sloane's A003173 : Heegner numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  4. "Sloane's A003215 : Hex (or centered hexagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  5. "Sloane's A125602 : Centered triangular numbers that are prime". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
  6. Roush, Gary (2008-06-02). "Statistics about the Vietnam War". Vietnam Helicopter Flight Crew Network. Archived from the original on 2009-12-07. Retrieved 2009-12-06. Assuming KIAs accurately represented age groups serving in Vietnam, the average age of an infantryman (MOS 11B) serving in Vietnam to be 19 years old is a myth, it is actually 22. None of the enlisted grades have an average age of less than 20.
  7. Center for Health Improvement (2008-06-02). "Minimum Age Increase". Archived from the original on 2009-07-22. Retrieved 2004-06-30. In Alabama, Alaska, and Utah, 19 years is the minimum age for sale of tobacco products
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