23 (twenty-three) is the natural number following 22 and preceding 24.

In mathematics

Twenty-three is the ninth prime number, the sequence continues 29, 31, 37, 41,... Twenty-three is also a factorial prime, a Sophie Germain prime, a safe prime, a Woodall prime, and a Smarandache-Wellin prime.

23 also has the distinction of being one of two integers that can't be expressed as the sum of 8 cubes (we allow 0^3 since zero is indeed an integer). The other integer is 239.

23 is a Wedderburn-Etherington number.

23 is a highly cototient number.

23 is the smallest prime that is not a twin prime.

23 is the ninth prime number, and 9 is 3 squared. This produces the interesting symmetry of 23-32.

In science

• The atomic number of vanadium
• The number of chromosomes in a human germline cell

In astronomy,

Messier object M23, a magnitude 6.0 open cluster in the constellation Sagittarius

The New General Catalogue object (http://www.ngcic.org/) NGC 23, a magnitude 12.0 barred spiral galaxy in the constellation Pegasus

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros1-175.html) of the solar eclipse series which began on -2145 May 7 and ended on -865 June 15. The duration of Saros series 23 was 1280.1 years, and it contained 72 solar eclipses.

The Saros number (http://sunearth.gsfc.nasa.gov/eclipse/LEsaros/LEsaros1-175.html) of the lunar eclipse series which began on -1843 February 14 and ended on -527 April 14. The duration of Saros series 23 was 1316.2 years, and it contained 74 lunar eclipses.

The 23rd moon of Jupiter is Carme

In other fields

Twenty-three is:

• In early 20th century United States slang, it meant to leave a place. (From the phrase 23 skiddoo ; the origins of the phrase are largely unknown).
• The sacred number (along with 17 and 5) of Eris, goddess of discord, according to the Principia Discordia; it is the number of the Illuminati.
• Like 13, sometimes considered unlucky or otherwise significant (as in the occult writings of Aleister Crowley and William S. Burroughs); see the 23 Enigma.
  • Robert Anton Wilson's book, Cosmic Trigger, lists 23 as a cosmic number with strong connections to arcane magic and synchronicity. Numerous people have claimed to see 23's everywhere (the 23 curse) prior to dying or some tragic incident.
• 23, a German movie about Karl Koch.
• A telegraphers' code meaning "line break".
• Michael Jordan's jersey number when he played for the Chicago Bulls basketball team.
• David Beckham's squad number at Real Madrid football (soccer) club.
• When mathematician John Forbes Nash suffered from schizophrenic delusions, he said that Life Magazine had run a cover story of him disguised as Pope John XXIII as his name was John and his favorite prime number was 23.
• The number of chromosomes in a human germline cell.
• The largest integer number of hours in a day.

• Historical years: 23 A.D., 23 B.C., or 1923

• Computers: decimal 23 is octal 027 and hexadecimal 0x17; The ASCII character set for decimal 23 is ETB