61 (number)

For the Cyrillic letter, see Ы.

← 60 61 62 →
← 60 61 62 63 64 65 66 67 68 69 → List of numbers Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	sixty-one
Ordinal	61st (sixty-first)
Factorization	prime
Prime	18th
Divisors	1, 61
Greek numeral	ΞΑ´
Roman numeral	LXI
Binary	1111012
Ternary	20213
Senary	1416
Octal	758
Duodecimal	5112
Hexadecimal	3D16

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

In mathematics

61 is the 18th prime number, and a twin prime with 59. It is the sum of two consecutive squares, $5^{2}+6^{2}.$ It is also a centered decagonal number. a centered hexagonal number, and a centered square number.

61 is the exponent of the ninth Mersenne prime, $2^{61}-1=2,305,843,009,213,693,951$. and the next candidate exponent for a potential fifth double Mersenne prime: $2^{2305843009213693951}-1\approx 1.695\times 10^{694127911065419641}.$

61 is the fourth cuban prime of the form $p={\tfrac {x^{3}-y^{3}}{x-y}}$ where $x=y+1$, and the forth Pillai prime since $8!+1$ is divisible by 61, but 61 is not one more than a multiple of 8. It is also 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, ...

61 is a unique prime in base 14, since no other prime has a 6-digit period in base 14, and palindromic in bases 6 (141₆) and 60 (11₆₀). It is the sixth up/down or Euler zigzag number.

61 is 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, ${\tfrac {p-1}{10}}$ times).

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

The exotic sphere $S^{61}$ is the last odd-dimensional sphere to contain a unique smooth structure; $S^{1}$, $S^{3}$ and $S^{5}$ are the only other such spheres.

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

See also: List of highways numbered 61

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 one of Philadelphia's tallest buildings at 61 stories
• The number of cadets on The Summerall Guards
• The number of points required to win a "standard" game of cribbage
• The maximum number of tables that can be joined in a single MariaDB or MySQL query

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.

References

• R. Crandall and C. Pomerance (2005). Prime Numbers: A Computational Perspective. Springer, NY, 2005, p. 79.