base 4 is a positional numeral system with four as its base. It uses 4 different digits for representing numbers. The digits for base 4 could be 0, 1, 2, and 3.

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.