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19 (nineteen) is the natural number following 18 and preceding 20

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

19 is the seventh Mersenne prime exponent.

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

19 is a centered triangular number, centered hexagonal number and a Heegner number.

The largest normal magic hexagon contains 19 hexagons.