23

23 is a natural number that comes after 22 and before 24. In decimal notation it is written as 23; in Roman numerals XXIII; in binary 10111; in hexadecimal 17.

Mathematically, 23 is prime; it is the ninth prime number. It is an odd prime and is a safe prime since (23−1)/2 = 11 is prime. It is also a Sophie Germain prime because 2×23+1 = 47 is prime.

In science, 23 is the atomic number of vanadium, a transition metal used mainly in alloys and catalysts. The chemical symbol is V. Vanadium was first identified in 1801 by Andrés Manuel del Río and later isolated; the element was named vanadium after Vanadis, a Norse goddess associated with beauty and strength.

In biology, humans have 23 pairs of chromosomes, for a total of 46 per somatic cell. The 23rd pair comprises the sex chromosomes, which determine biological sex as XX or XY.

Other uses include the Telnet protocol, which historically runs over TCP port 23. Messier 23 (M23) is a star cluster in the constellation Sagittarius. In culture, the number 23 is the focus of various theories and references, such as the 23 enigma, and is also a notable jersey number for several well-known athletes.