A043920 Numbers n such that 1 and 5 occur juxtaposed in the base 7 representation of n but not of n+1.

12, 36, 61, 90, 110, 134, 159, 183, 208, 232, 258, 281, 306, 330, 355, 379, 404, 433, 453, 477, 502, 526, 551, 575, 636, 649, 673, 698, 722, 747, 776, 796, 820, 845, 869, 894, 918, 944, 967, 992, 1016, 1041, 1065, 1090, 1119