23

Number
$23$ (twenty-three) is:


 * The $9$th prime number, after $2, 3, 5, 7, 11, 13, 17, 19$


 * The first of the first pair of consecutive prime numbers which differ by $6$:
 * $23, 29: 29 - 23 = 6$


 * The first of the only two positive integers needing as many as $9$ positive cubes to express it:
 * $23 = 2^3 + 3^3 + 1^3 + 1^3 + 1^3 + 1^3 + 1^3 + 1^3 + 1^3$
 * The other is $239$.

Also see

 * Hilbert-Waring Theorem: Cubes