base 18 is a positional numeral system with eighteen as its base. It uses 18 different digits for representing numbers. The digits for base 18 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, and h.

base 26 is a positional numeral system with twenty-six as its base. It uses 26 different digits for representing numbers. The digits for base 26 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, and p.