The decimal numeral system (also called base-ten positional numeral system, and occasionally called denary) is the standard system for denoting integer and non-integer numbers. It has ten as its base.
base 21
base 21 is a positional numeral system with twenty-one as its base. It uses 21 different digits for representing numbers. The digits for base 21 could be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, h, i, j, and k.