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 17
base 17 is a positional numeral system with seventeen as its base. It uses 17 different digits for representing numbers. The digits for base 17 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, and g.