Base-20 (also known as vigesimal) number system uses 20 symbols to code information. Most commonly, these symbols are, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 'A to J' (or alternatively 'a to j').
Base-9 (also called nonary) number system uses nine symbols to code information. Most commonly, these symbols are, 0, 1, 2, 3, 4, 5, 6, 7 and 8.