# 19 (number)

"Nineteen" redirects here. For other uses, see 19 (disambiguation).
 ← 18 19 20 →
Cardinal nineteen
Ordinal 19th
(nineteenth)
Factorization prime
Divisors 1, 19
Roman numeral XIX
Binary 100112
Ternary 2013
Quaternary 1034
Quinary 345
Senary 316
Octal 238
Duodecimal 1712
Vigesimal J20
Base 36 J36

19 (nineteen) 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, as sounding very similar. When carefully enunciated, they differ in which syllable is stressed: 19 /nnˈtn/ vs 90 /ˈnnti/. However, in dates such as 1999, and when contrasting numbers in the teens and when counting, such as 17, 18, 19, the stress shifts to the first syllable: 19 /ˈnntn/. In a 24-hour clock, the nineteenth hour is in conventional language called seven or seven o'clock.

## Mathematics

19 is the 8th prime number. The sequence continues 23, 29, 31, 37, ... .

19 is the seventh Mersenne prime exponent.[1]

19 is the fifth happy number[2] and the third happy prime.[3]

19 is the aliquot sum of two odd discrete semiprimes, 65 and 77 and is the base of the 19-aliquot tree.

19 is the maximum number of fourth powers needed to sum up to any natural number. It is the fourth value of g(k).

19 is the lowest prime centered triangular number,[4] a centered hexagonal number[5] and a Heegner number.[6]

The only non-trivial normal magic hexagon contains 19 hexagons (the other being 1).

19 is the first number with more than one digit that can be written from base 2 to base 19 using only the digits 0 to 9; the other number is 20.[7]

## Technology

19 is The TCP/IP port used for chargen.

## 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...
• Quran code: There have been claims that patterns of the number 19 are present an unusual number of times in the Qur'an.
• 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).

### Baha'i faith

In the Bábí and Bahá'í 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 (an assertion which is widely disputed).[8] 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.
• With a similar name and anti-Vietnam War theme, "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, written by members Walter Becker and Donald Fagen, and released on their 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.

## 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).
• 19 is the command in Age of Empires for the laughing emote.
• 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 "19 points."
• In Ecuadorian card game "40", when counting the amount 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 minimum age that is legal to buy tobacco products in the states Alabama, Alaska, New Jersey, Utah and several counties in New York including Nassau, and Onondaga.[9]
• 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.
• This is the minimum age to marry in the state of Nebraska.
• 19 is the average age of a US combat soldier in the Vietnam War.

## References

1. "Sloane's A000043 : Mersenne exponents". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
2. "Sloane's A007770 : Happy numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
3. "Sloane's A035497 : Happy primes". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
4. "Sloane's A125602 : Centered triangular numbers that are prime". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
5. "Sloane's A003215 : Hex (or centered hexagonal) numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
6. "Sloane's A003173 : Heegner numbers". The On-Line Encyclopedia of Integer Sequences. OEIS Foundation. Retrieved 2016-05-31.
7. Sequence A131646 in The On-Line Encyclopedia of Integer Sequences
8. Roush, Gary (2008-06-02). "Statistics about the Vietnam War". Vietnam Helicopter Flight Crew Network. Archived from the original on 2009-12-06. 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.
9. 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