# 51 (number)

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**51** (**fifty-one**) is the natural number 51 following 50 and preceding 52.

## In mathematics

**Fifty-one** is the 14th discrete biprime and the 5th in the {3.q} semiprime family having the prime factors (3.17). The aliquot sum of 51 is 21, itself a discrete biprime. 51 is the 4th member of the 11-aliquot tree with the sequence (51, 21, 11, 1, 0).

51 is a pentagonal number as well as a centered pentagonal number (one of the few numbers to be both) and an 18-gonal number and a Perrin number. It is also 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.

Since the greatest prime factor of 51^{2} + 1 = 2602 is 1301, which is clearly more than 51 twice, 51 is a Størmer number.

There are 51 different cyclic Gilbreath permutations on 10 elements,^{[1]} and therefore there are 51 different real periodic points of order 10 on the Mandelbrot set.^{[2]}

## In sports

Template:As of, the highest number of international test cricket centuries scored by an individual is 51. It is the world record, held by India's Sachin Ramesh Tendulkar.^{[3]}

## In other fields

51 is:

- The atomic number of antimony.
- The code for international direct dial phone calls to Peru

## See also

- 51, a year in the Julian calendar
- List of highways numbered 51
- The model number of the P-51 Mustang WWII fighter aircraft
- Area 51, a parcel of U.S. military-controlled land in southern Nevada, apparently containing a secret aircraft testing facility
*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.
- 51 (film), a 2011 American horror film
- "Fifty-One", an episode of
*Breaking Bad* - Pastis 51, often just called "51", is a brand of pastis owned by Pernod Ricard.

## References

- ↑ Template:SloanesRef
- ↑ {{#invoke:citation/CS1|citation |CitationClass=citation }}.
- ↑ Template:Cite news