51 (number)

For the year, see 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	$3 \cdot 17$
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.

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 +193 July 31. The duration of Saros series 51 was 1298.1 years, and it contained 73 lunar eclipses.

In sports

• Las Vegas 51s, a minor league baseball team of the Pacific Coast League
• The jersey number 51 has been retired by a number of North American sports teams in honor of past playing greats:
  • In the National Football League:
    • The Carolina Panthers for Sam Mills
    • The Chicago Bears, for Hall of Famer Dick Butkus
  • In Major League Baseball, the San Diego Padres for Trevor Hoffman

In other fields

• List of highways numbered 51
• 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
• 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
• "51st anniversary" song by Jimi Hendrix
• "Come in Number 51, Your Time is Up" song by Pink Floyd
• "Number 51" is referenced in the song "The Happening," by The Pixies
• Parker 51 fountain pen, introduced in 1941
• A brand of pastis (anise liqueur) manufactured by Pernod Ricard
• 51, Doc Hudson's racecar number in Cars (film)
• "Cachaça 51" is the brand name of a cachaça produced by a Companhia Müller de Bebidas in Pirassununga, São Paulo, Brasil
• Squier '51, a guitar made by Fender's second brand, Squier
• The number of the French department Marne
• Suda51 is the nickname of Goichi Suda, the CEO of Grasshopper Manufacturer.
• Year identifier used on motor vehicles registered in the UK between September 1, 2001 and February 28, 2002
• The station number and apparatus numbers from the TV series Emergency!
• 51 (film), a 2011 American horror film

Historical years

51 A.D., 51 BC, 1951, 2051, etc.