Dozenal Numbers

Intro Characters: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, X, £, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 1X 1£, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 2X, 2£, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 3X, 3£, 40.