61 (sixty-one) is the natural number following 60 and preceding 62.

In mathematics

61 is:

• the 18th prime number.
• a twin prime with 59.
• a cuban prime of the form p = x³ − y³/x − y, where x = y + 1.^[1]
• the smallest proper prime, a prime p which ends in the digit 1 in base 10 and whose reciprocal in base 10 has a repeating sequence with length p − 1. In such primes, each digit 0, 1, ..., 9 appears in the repeating sequence the same number of times as does each other digit (namely, p − 1/10 times).^[2]: 166
• the exponent of the 9th Mersenne prime.^[3] (2⁶¹ − 1 = 2,305,843,009,213,693,951)
• the sum of two squares, 5² + 6².
• a centered square number.^[4]
• a centered hexagonal number.^[5]
• a centered decagonal number.^[6]
• the sixth Euler zigzag number (or Up/down number).
• a unique prime in base 14, since no other prime has a 6-digit period in base 14.
• a Pillai prime since 8! + 1 is divisible by 61 but 61 is not one more than a multiple of 8.^[7]
• a Keith number, because it recurs in a Fibonacci-like sequence started from its base 10 digits: 6, 1, 7, 8, 15, 23, 38, 61...^[8]
• palindromic in bases 6 (141₆) and 60 (11₆₀)

In the list of Fortunate numbers, 61 occurs thrice, since adding 61 to either the tenth, twelfth or seventeenth primorial gives a prime number^[9] (namely 6,469,693,291; 7,420,738,134,871; and 1,922,760,350,154,212,639,131).

In science

• The chemical element with the atomic number 61 is promethium.

Astronomy

• Messier object M61, a magnitude 10.5 galaxy in the constellation Virgo
• The New General Catalogue object NGC 61, a double spiral galaxy in the constellation Cetus
• 61 Ursae Majoris is located about 31.1 light-years from the Sun. [1]
• 61 Cygni was christened the "Flying Star" in 1792 by Giuseppe Piazzi (1746–1826) for its unusually large proper motion. [2]

In other fields

Sixty-one is:

• The number of the French department Orne
• The code for international direct dial phone calls to Australia
• 61*, a 2001 baseball movie directed by Billy Crystal
• Highway 61 Revisited is a Bob Dylan album
• The Highway 61 Blues Festival occurs annually in Leland, Mississippi
• Highway 61 is a 1991 film set on U.S. Route 61
• U.S. Route 61 is the highway that inspired so much attention on "Highway 61"
• Part 61 is a law created by the FAA regarding medical exams. This law has often come under attack by AOPA.
• The P-61 is the Northrop-designed fighter first designated as the XP-61. It first flew on May 26, 1942. It is also known as the Black Widow as it was the first fighter aircraft designed to be a night fighter
• Sixty 1 is a brand tobacco produced by Nationwide Tobacco
• 61A is the London address of Margot Wendice (Grace Kelly) and Tony Wendice (Ray Milland) in the movie Dial M for Murder
• 1 Liberty Place is Philadelphia's tallest building at 61 stories
• The number of cadets on The Summerall Guards
• The number of points required to win a "standard" game of cribbage^[10]
• The maximum number of tables that can be joined in a single MariaDB or MySQL query^[11]

In sports

• New York Yankees right fielder Roger Maris hit 61 home runs in 1961, breaking Babe Ruth's single-season record until it was surpassed in 1998 by Mark McGwire and Sammy Sosa.
• Nolan Ryan and Tom Seaver each had 61 career shutouts
• Hockey great Wayne Gretzky holds or shares 61 NHL records (40 for regular season, 15 for Stanley Cup playoff, and 6 for All-Star Games)
• Rotation, a variation of pool, is sometimes called 61
• Richie Evans' NASCAR Whelen Modified Tour car number was 61 until his death in 1985
• The number of the laps of the first Formula One night race, Singapore Grand Prix.