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').
Base-7 (aka septenary) number system uses seven symbols to code information. Most commonly, these symbols are, 0, 1, 2, 3, 4, 5 and 6.