19 (number)


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

Mathematics

19 is the 8th prime number, the seventh Mersenne prime exponent, and the second base-10 repunit prime exponent. 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. In addition, 19 is a Heegner number and a centered hexagonal number. 19 is also a centered triangular number, 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

Islam

In the Bábí and Bahá'í faiths, a group of 19 is called a Váhid, a Unity. The numerical value of this word in the Abjad numeral system is 19.