51

← 50 52 → 51
← 50 51 52 53 54 55 56 57 58 59 → List of numbers — Integers 0 10 20 30 40 50 60 70 80 90 →
Cardinal	fifty-one
Ordinal	51st (fifty-first)
Factorization
Divisors	1, 3, 17, 51
Roman numeral	LI
Binary	1100112
Octal	638
Duodecimal	4312
Hexadecimal	3316

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

Look up fifty-one in Wiktionary, the free dictionary.

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 51² + 1 = 2602 is 1301, which is clearly more than 51 twice, 51 is a Størmer number.

In science

• The atomic number of antimony.

Astronomy

• Messier object M51, a magnitude 8.0 spiral galaxy in the constellation Canes Venatici, also known as the Whirlpool Galaxy
• The New General Catalogue object NGC 51, a spiral galaxy in the constellation Andromeda
• The Saros number of the solar eclipse series which began on -1407 September 2 and ended on 108 February 29. The duration of Saros series 51 was 1514.5 years, and it contained 85 solar eclipses. The Saros number of the lunar eclipse series which began on -1105 June 13 and ended on 211 August 12. The duration of Saros series 51 was 1316.2 years, and it contained 74 lunar eclipses.

In sports

• Las Vegas 51s, a minor league baseball team of the Pacific Coast League

In other fields

Area 51

Fifty-one is:

• The code for international direct dial phone calls to Peru
• 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
• Part of the title of a collection of stories by Lord Dunsany, Fifty-One Tales
• Washington D.C. and Puerto Rico often mentioned as the future "51st State"
• "51st anniversary" song by Jimi Hendrix
• "Come in Number 51, Your Time is Up" song by Pink Floyd
• Bob Dylan: Highway 51 Blues and the name of a band
• The Parker 51, introduced in 1941, may well be the most famous fountain pen ever made
• A brand of pastis (anise liqueur) manufactured by Pernod Ricard
• "Cachaça 51" is the brand name of a cachaça produced by a Companhia Müller de Bebidas in Pirassununga, São Paulo, Brasil.
• The '51 is a guitar made by Fender's second brand, Squier. It is notable for being one of only a few original models produced by the marque.
• The number of the French department Marne
• The number of the Orton ATC Squadron ^[1], number of the old RAF squadron ^[2] and number of the RAF Regiment unit ^[3]

• Year identifier used on motor vehicles registered in the UK between 1 September 2001 and 28 February 2002

Historical years

51 A.D., 51 B.C., 1951, 2051, etc.

References

Footnotes