base 15 is a positional numeral system with fifteen as its base. It uses 15 different digits for representing numbers. The digits for base 15 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, and e.

base 23 is a positional numeral system with twenty-three as its base. It uses 23 different digits for representing numbers. The digits for base 23 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, h, i, j, k, l, and m.