# 23 (number)

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

 << 20 21 22 23 24 25 26 27 28 29 >> Cardinal twenty-three Ordinal twenty-third Factorization prime Roman numeral XXIII Binary 10111 Hexadecimal 17
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## In mathematics

Twenty-three is the ninth prime number, the sequence continues 29, 31, 37, 41,... Twenty-three is also the fifth factorial prime, the fifth Sophie Germain prime, the fourth safe prime, the second Woodall prime, and the second 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 odd 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

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:

• Art and Cultures
• Countries of the World (http://www.academickids.com/encyclopedia/index.php/Countries)
• Space and Astronomy