19 (number)

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


Cardinal	19 nineteen
Ordinal	19th nineteenth
Factorization	prime
Divisors	1, 19
Roman numeral	XIX
Binary	10011
Hexadecimal	13

In mathematics

Nineteen is the 8th smallest prime number. The sequence continues 23, 29, 31, 37... 19 is the seventh Mersenne prime exponent.

It is also a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 1, 9, 10, 19...

With respect to divisibility, nineteen has a very simple test: 19 divides 100a + b if and only if it divides a + 4b.

Nineteen is a centered triangular number, centered hexagonal number, and an octahedral number.

Every positive integer is the sum of at most nineteen fourth powers (see Waring's problem).

The decimal expansion of 1/19 has a period of maximum length: 18 digits.

Nineteen is a Heegner number and a strictly non-palindromic number.

19 is the fourth alternating factorial.

In science

The atomic number of potassium.

Astronomy

Messier object M19, a magnitude 8.5 globular cluster in the constellation Ophiuchus

The New General Catalogue object NGC 19, a barred spiral galaxy in the constellation Andromeda

The number of years of the Metonic cycle

The Saros number of the solar eclipse series which began on 2333 BC June 15 and ended on 1035 BC August 1. The duration of Saros series 19 was 1298.1 years, and it contained 73 solar eclipses.

The Saros number of the lunar eclipse series which began on 2031 BC March 24 and ended on 731 BC May 11. The duration of Saros series 19 was 1298.1 years, and it contained 73 lunar eclipses.

In religion

The number of years in each cycle of the intercalated Hebrew calendar, in which 7 of the 19 years are leap years
The number of angels guarding Hell according to the Qur'an: "Over it is nineteen" (74:30)
The number of surat Maryam in the Qur'an
The number of letters in the basmala formula "In the Name of God, the Merciful, the Compassionate" in Arabic
A number encoded in the Qur'an as claimed by Dr. Rashad Khalifa, a biochemist and Qur'an Alone Muslim from the USA, about the Qur'an
The Bahá'í calendar is structured such that a year contains 19 months of 19 days each, as well as a 19-year cycle and a 361-year (19x19) supercycle. The Báb and his disciples formed a group of 19, and there were 19 Apostles of Bahá'u'lláh.
Nineteen sometimes has been considered significant in astrology or esoteric religion because it is the sum of the number of the constellations of the zodiac (12) and the number of the classically-known "planets" (7, including the sun and moon).

In music

"19" is a 1985 hit song by Paul Hardcastle, with a strong anti-war message, based on 19 reportedly being the average age of United States soldiers killed in the Vietnam War (this is widely disputed). The song was parodied by British satirist Rory Bremner as N-n-nineteen, Not Out, the title referring to the English cricket team's risible performance against the West Indies in the previous year.

I Was Only 19 (A Walk in the Light Green), by the Australian group Redgum reached number one on the Australian charts in 1983, and a hip-hop version of the song produced by The Herd was voted in the top ten songs of 2005 by listeners of radio station Triple J.

Other songs with the number 19 in their titles:

"Nineteen" by the Old 97's

"Hey, Nineteen" by Steely Dan

"19th Nervous Breakdown" by the Rolling Stones

"Nineteen Forever" by Joe Jackson

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.

In other fields

Nineteen is

The nineteenth state to enter the Union was Indiana
Part of the name of a breakfast cereal: Product 19
The Soviet submarine K-19 was the first Soviet nuclear ballistic submarine
I-19 is the designation for a US interstate highway in Arizona
19 years is very close to 235 lunations. See Metonic cycle
A significant recurring number (which comes to denote a sense of unreality and foreboding) in the Dark Tower novels by author Stephen King
In golf the "19th hole" is the clubhouse bar. In miniature golf it is an extra hole on which the winner earns an instant prize
A number encoded in Chemistry as claimed by Dr. Peter Plichta, a German chemist Also see [http://www.submission.org/miracle/19-chemistry.html for Plichta's claimed code-19 in chemistry
The retired baseball jersey number of Robin Yount
19 x 19 is also the standard size of a Go Board
It is not possible to earn a score of 19 in a single hand of cribbage
19 is the other half of 23 making the total : 42

Historical years

A.D. 19, 19 B.C., 1919, 2019, etc.

External links

Integers

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