base 11 is a positional numeral system with eleven as its base. It uses 11 different digits for representing numbers. The digits for base 11 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and a.
hexadecimal (base 16)
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).