65 (number)

65 is the natural number following 64 and preceding 66.

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:

<math> \begin{bmatrix}

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{bmatrix}. <math>

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.

In science

• The atomic number of terbium, a lanthanide

In astronomy,

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.
• The designation of Interstate 65, a freeway that runs from Alabama to Indiana.
• The code for international direct dial phone calls to Singapore.
• The standard age for retirement in the UK, Germany and other countries.
• The registry of the U.S. Navy's nuclear aircraft carrier USS Enterprise (CVN-65).
• The year AD 65, 65 BC, or 1965.