A044560 Numbers n such that string 5,6 occurs in the base 7 representation of n but not of n+1.

41, 90, 139, 188, 237, 293, 335, 384, 433, 482, 531, 580, 636, 678, 727, 776, 825, 874, 923, 979, 1021, 1070, 1119, 1168, 1217, 1266, 1322, 1364, 1413, 1462, 1511, 1560, 1609, 1665, 1707, 1756, 1805, 1854, 1903, 1952, 2057