61 (number)

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


Cardinal	61 sixty-one
Ordinal	61st sixty-first
Factorization	prime
Roman numeral	LXI
Binary	111101
Hexadecimal	3D

In mathematics

It is the 18th prime number. The previous is 59, with which it comprises a twin prime. Sixty-one is a cuban prime of the form

p = (x^3 - y^3) / (x - y), x = y + 1

Sixty-one might be the largest prime that divides the product of the next two primes plus 1. If there is a larger such prime, it would have to be greater than 179424673.

Sixty-one is the sum of two squares, 5² + 6², and it is also a centered square number, a centered hexagonal number and a centered decagonal number.

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...

In science

In the periodic table

The chemical element with the atomic number 61 (promethium), a lanthanide, is the element with the secondary lowest ordinal number, which does not possess any stable isotopes. The promethium preceding element with atomic number 60 (neodymium) and the promethium following element 62 (samarium) have all stable isotopes.

In 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 Pisces

The Saros number of the solar eclipse series which began on -973 May 10 and ended on 289 June 5. The duration of Saros series 61 was 1262.1 years, and it contained 71 solar eclipses.

The Saros number of the lunar eclipse series which began on -870 October 20 and ended on 609 March 26. The duration of Saros series 61 was 1478.4 years, and it contained 83 lunar eclipses.

61 Ursae Majoris is located about 31.1 light-years from Sol.^*

61 Cygni was christened the "Flying Star" in 1792 by Giuseppe Piazzi (1746-1826) for its unusually large proper motion. ^*

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.
The year AD 61, 61 BC, or 1961.
A number often related to Colonel Campbell's insane speech in Sons of Liberty.
Highway 61 Blues Festival is in June in Leland, MS. ^*
Scout Pack and Troop 61 both serve the town of Mansfield, Connecticut.^*
Troop 61 is one of the oldest and best-known Boy Scout troops in the Kansas City area. ^*
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.^*
Psalm 61 ^*

Reference

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