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19 (Number)19 (nineteen) is the natural number following 18 and preceding 20. 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 100*a+b if and only if it divides a+4*b. 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. In science In 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 Saros number of the solar eclipse series which began on -2333 June 15 and ended on -1035 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 March 24 and ended on -733 May 11. The duration of Saros series 19 was 1298.1 years, and it contained 73 lunar eclipses.
In music "19" is a 1985 hit song by Paul Hardcastle, with a strong anti-war message, based on 19 being the average age of soldiers in the Vietnam war. Other songs with the number in their titles include "Nineteen" by the Old 97's and "Hey, Nineteen" by Steely Dan. In other fields Nineteen is External link 1 9
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