Base-16 (also known as hexadecimal) number system uses 16 symbols to code information. Most commonly, these symbols are, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 'A to F' (or alternatively 'a to f').
Base-4 (aka quaternary) number system uses four symbols to code information. Most commonly, these symbols are, 0, 1, 2 and 3.