19 (number)

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

Mathematics

19 is the eighth prime number. 19 forms a twin prime pair with 17, a cousin prime pair with 23, and a sexy prime pair with 13. 19 is a strictly non-palindromic number in any base, 19 is the maximum number of fourth powers needed to sum up to any natural number (see, Waring's problem). There are 19 compositions of 8 into distinct parts.

There are 19 nodes in regular hexagon with all diagonals drawn is nineteen. The only nontrivial normal magic hexagon is composed of nineteen cells, where every diagonal of consecutive hexagons has sums equal to 38, or twice 19. A hexaflexagon is a strip of nineteen alternating triangular faces that can flex into a regular hexagon, such that any two of six colorings on triangles can be oriented to align on opposite sides of the folded figure.

${\displaystyle {\tfrac {1}{19}}}$ can be used to generate the first full, non-normal prime reciprocal magic square in decimal whose rows, columns and diagonals — in a 18 x 18 array — all generate a magic constant of 81 = 9².

Science

• The James Webb Space Telescope's optical elements are in an array of 19 hexagons, wherein 18 segmented primary mirrors focus light into a centered secondary mirror situated above the collecting mirrors, that in-turn reflects back onto the telescope's central imagers. It is a shape akin to the order-3 magic hexagon.
• The Metonic cycle is almost exactly 19 years long.

Music

• 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.^{[citation needed]}

Religion

Literature

Stephen King's eight-book epic The Dark Tower saga employs the number 19 in books The Dark Tower: The Gunslinger, The Dark Tower V: Wolves of the Calla, The Dark Tower VI: Song of Susannah, The Dark Tower VII: The Dark Tower, and The Wind Through the Keyhole as a mysterious and important number. They refer to the "ka-tet of 19", "Directive Nineteen," many names add up to 19, 19 seems to permeate every aspect of Roland and his traveler's lives. In addition, the number ends up being a powerful key.

Games

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 "a 19 hand".

In sports

In golf, the '19th hole' is the clubhouse bar and in match play, if there is a tie after 18 holes, an extra hole(s) is played. In miniature golf, it is an extra hole on which the winner earns an instant prize.

Age 19

• In four countries (Algeria, South Korea, United States (Alabama and Nebraska), and Canada), 19 is the age of majority.
• In two countries (South Korea and Canada), 19 is the minimum legal drinking age.
• In three countries (Algeria, South Korea, and Canada), 19 is the minimum legal smoking age.
• The minimum age for the NBA draft is 19 years old.

References

External links

Wikimedia Commons has media related to 19 (number).

Look up nineteen in Wiktionary, the free dictionary.

• Number 19 at the Database of Number Correlations Archived 2018-11-15 at the Wayback Machine
• Prime Curios for the number 19