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 NGC 23 , a magnitude 12.0 barred spiral galaxy in the constellation Pegasus

The Saros number 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 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

Occult significance

• 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 lucky 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 enormous success and fruitfulness.
  • In many other of Wilson's works (especially The Illuminatus! Trilogy and Principia Discordia) 23 is given special importance. Many Discordians use this number for any number of purposes.

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).
• 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