64 is the natural number following 63 and preceding 65.

In mathematics

Sixty-four is the square of 8 and the cube of 4. It is the lowest positive power of two that is adjacent to neither a Mersenne prime nor a Fermat prime. It is also a dodecagonal number and a centered triangular number. 64 is a self number.

In science

• The atomic number of gadolinium, a lanthanide

In astronomy,

Messier object M64, a magnitude 9.0 galaxy in the constellation Coma Berenices, also known as the Black Eye Galaxy.

The New General Catalogue object (http://www.ngcic.org/) NGC 64, a barred spiral galaxy in the constellation Cetus

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -832 April 11 and ended on 430 May 8. The duration of Saros series 64 was 1262.1 years, and it contained 71 solar eclipses.

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -801 August 9 and ended on 714 February 4. The duration of Saros series 64 was 1514.5 years, and it contained 85 lunar eclipses.

In other fields

Sixty-four is also:

• In some computer programming languages, the size in bits of certain data types.
• In China, "64 incident" refers to the Tiananmen Square protests of 1989 which happened on 4 June 1989.
• In chess or draughts, the total number of black and white squares on the game board.
• The code for international direct dial calls to New Zealand.
• The designation of US Interstate 64, a freeway from Missouri to Virginia.
• The subject of the Beatles song "When I'm Sixty-Four"
• The registry of the U.S. Navy's aircraft carrier USS Constellation (CV-64)
• The number of Braille characters in the old 6-dot system.
• The year AD 64, 64 BC, or 1964.
• In video games, the Nintendo 64 video game console and the Commodore 64. Since 1996, the number 64 is usually the abbreviation or slang for Nintendo 64.
• The maximum number of strokes in any Chinese character.