65 (number)
Encyclopedia : 6 : 65 : 65N : 65 (number)
65 (sixty-five) is the natural number following 64 and preceding 66.
| Cardinal | 65 sixty-five |
| Ordinal | 65th sixty-fifth |
| Factorization | [5 \cdot 13] |
| Roman numeral | LXV |
| Binary | 1000001 |
| Hexadecimal | 41 |
In mathematics
Sixty-five is an octagonal number. It is also a Cullen number. Given 65, the Mertens function returns 0.This number is the magic constant of 5 by 5 magic square:
[\begin 17 & 24 & 1 & 8 & 15 \\ 23 & 5 & 7 & 14 & 16 \\ 4 & 6 & 13 & 20 & 22 \\ 10 & 12 & 19 & 21 & 3 \\ 11 & 18 & 25 & 2 & 9\end.]
This number is also the magic constant of n-Queens Problem for n = 5.
65 can be expressed as a sum of two squares in two ways, 65 = 82 + 12 = 72 + 42.
It appears in the Padovan sequence, preceded by the terms 28, 37, 49 (it is the sum of the first two of these).
In science
- The atomic number of terbium, a lanthanide
- Messier object M65, a magnitude 10.5 galaxy in the constellation Leo
- The New General Catalogue [object] NGC 65, a spiral galaxy in the constellation Cetus
- The Saros [number] of the solar eclipse series which began on -749 April 24 and ended on 513 May 20. The duration of Saros series 65 was 1262.1 years, and it contained 71 solar eclipses.
- The Saros [number] of the lunar eclipse series which began on -736 August 11 and ended on 797 February 16. The duration of Saros series 65 was 1532.5 years, and it contained 86 lunar eclipses.
In other fields
Sixty-five is also:
- A common speed limit, in miles per hour, for freeways in many U.S. states, primarily in the eastern portion of the United States (in the western portion, the common limit is 70 and in some places 75).
- The designation of Interstate 65, a freeway that runs from Alabama to Indiana.
- The code for international direct dial phone calls to Singapore.
- The traditional age for retirement in the UK, Germany and other countries. It was previously the age at which a person in the United States could retire with full Social Security benefits; however, recent changes in the law have increased this age for younger workers due to improvements in life expectancy.
- The registry of the U.S. Navy's nuclear aircraft carrier USS Enterprise (CVN-65).
- The year AD 65, 65 BC, or 1965.
- 65 is the minimum grade required to pass an exam, or class in many areas.
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