Erasing even digits
(Dall-e creation ) We S start with a(1) = k , multiply k by 3 and iterate. When even digits appear in the result, we erase them, concatenate what is left and go on. S = 1 , 3, 9, (2)7, (2) 1 , loop S = 2, (6) END S = 4, 1 (2), ... loop S = 5 , 15, (4) 5 , loop S = 6, 1 (8), ... loop S = 8, (24) END S = 10, 3 (0), ... loop S = 11, 33, 99, (2)97, (2)91, (2)73, (2)19, 57, 171, 513, 1539, (46)17, 51, 153 , (4)59, 177, 531, 1593, (4)779, (2)337, 1(0)11, 333, 999, (2)997, (2)991, (2)973, (2)919, (2)757, (22)71, (2)13, 39, 117, 351, 1 (0) 53 , loop S = 12, 3(6), ... loop S = 14, (42) END S = 16, (48) END S = 18, 5(4), ... loop S = 20, (60) END S = 21, (6)3, ... loop S = 22, (66) END S = 23, (6)9, ... loop S = 24, 7(2), ... loop S = 25, 75, (22)5, ... loop S = 26, 7(8), ... loop S = 27, (8)1, ... loop S = 28, (84) END S = 29, (8)7, ... loop S = 30, 9(0), ... loop S = 31, 93, (2)79, (2)37, 111, ... loop S = 32, 9(6), ... loop S = 34, 1(02), ... loop S = 35, 1(0)5, ... loop S = 36, 1(08), ... l