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.
quinary (base 5)
Quinary (base-5 or pental) is a numeral system with five as the base. A possible origination of a quinary system is that there are five fingers on either hand.