It is a happy number.
23 is nontrivially palindromic in base 3.
23 is an esthetic number in base 3, base 5, base 7, base 10 and base 11, because in such bases it adjacent digits differ by 1.
It is a weak prime.
23 is a truncatable prime.
It is a cyclic number.
It is a Sophie Germain prime.
It is a Chen prime.
It is a magnanimous number.
It is an alternating number because its digits alternate between even and odd.
It is a Kynea number, being equal to (22 + 1)2 - 2.
23 is an undulating number in base 3.
It is a plaindrome in base 4, base 6, base 8, base 9, base 10, base 12, base 13, base 14, base 15 and base 16.
It is a nialpdrome in base 5, base 7 and base 11.
It is a congruent number.
It is a panconsummate number.
Being equal to 3×23-1, it is a Woodall number.
23 is an equidigital number, since it uses as much as digits as its factorization.
23 is an evil number, because the sum of its binary digits is even.
The square root of 23 is about 4.7958315233. The cubic root of 23 is about 2.8438669799.