The vigesimal or base 20 numeral system is based on twenty (in the same way in which the decimal numeral system is based on ten).
base 13
base 13 is a positional numeral system with thirteen as its base. It uses 13 different digits for representing numbers. The digits for base 13 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, and c.