A044528 Numbers n such that string 1,2 occurs in the base 7 representation of n but not of n+1.

9, 58, 69, 107, 156, 205, 254, 303, 352, 401, 412, 489, 499, 548, 597, 646, 695, 744, 755, 793, 842, 891, 940, 989, 1038, 1087, 1098, 1136, 1185, 1234, 1283, 1332, 1381, 1430, 1441, 1479, 1528, 1577, 1626, 1675, 1724, 1773