A044779 Numbers n such that string 6,6 occurs in the base 10 representation of n but not of n+1.

66, 166, 266, 366, 466, 566, 669, 766, 866, 966, 1066, 1166, 1266, 1366, 1466, 1566, 1669, 1766, 1866, 1966, 2066, 2166, 2266, 2366, 2466, 2566, 2669, 2766, 2866, 2966, 3066, 3166, 3266, 3366, 3466, 3566, 3669, 3766, 3866