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-24 number system uses 24 symbols to code information. Most commonly, these symbols are, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 'A to N' (or alternatively 'a to n').