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# 23 (number)

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

 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 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

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

## In other fields

Twenty-three is:

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

03-10-2013 05:06:04