the 6th
Motzkin number, telling the number of ways to draw non-intersecting
chords between any six points on a circle's boundary, no matter where the points may be located on the boundary.[4]
a
Perrin number,[5] coming after 22, 29, 39 in the sequence (and the sum of the first two)
a
Størmer number, since the greatest prime factor of 512 + 1 = 2602 is 1301, which is substantially more than 51 twice.[6]
The model number of the
P-51 Mustang World War II fighter aircraft
Area 51, a parcel of U.S. military-controlled land in southern Nevada, apparently containing a secret aircraft testing facility
Photo 51, an X-ray image of key importance in elucidating the structure of DNA in the 1950s
Fifty-One Tales, part of the title of a collection of stories by Lord Dunsany
"
51st State", any future US state, usually referring to Washington, D.C., or Puerto Rico. Occasionally used in commentary to refer to non-US entities (such as
Alberta) adopting US-like policies or seeking to become part of the US.
^Diaconis, Persi;
Graham, Ron (2012), "Chapter 5: From the Gilbreath Principle to the Mandelbrot Set", Magical Mathematics: the mathematical ideas that animate great magic tricks, Princeton University Press, pp. 61–83.