51 (number)
Natural number
From Wikipedia, the free encyclopedia
51 (fifty-one) is the natural number following 50 and preceding 52.
Look up fifty-one in Wiktionary, the free dictionary.
In mathematics
Fifty-one is
- a pentagonal number[1] as well as a centered pentagonal number[2] and an 18-gonal number[3]
- 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]
- There are 51 different cyclic Gilbreath permutations on 10 elements,[7] and therefore there are 51 different real periodic points of order 10 on the Mandelbrot set.[8]
- Since 51 is the product of the distinct Fermat primes 3 and 17, a regular polygon with 51 sides is constructible with compass and straightedge, the angle π/51 is constructible, and the number cos π/51 is expressible in terms of square roots.