61 (number)
61 (sixty-one) is the natural number following 60 and preceding 62.
| |||
| Cardinal | 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 = (x3 − y3) / (x − y),x = y + 1. 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
- The atomic number of promethium, a lanthanide
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.
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.