A044780 Numbers n such that string 6,7 occurs in the base 10 representation of n but not of n+1.

67, 167, 267, 367, 467, 567, 667, 679, 767, 867, 967, 1067, 1167, 1267, 1367, 1467, 1567, 1667, 1679, 1767, 1867, 1967, 2067, 2167, 2267, 2367, 2467, 2567, 2667, 2679, 2767, 2867, 2967, 3067, 3167, 3267, 3367, 3467, 3567