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.
quaternary (base 4)
Quaternary is the base-4 numeral system. It uses the digits 0, 1, 2 and 3 to represent any real number.