A044440 Numbers n such that string 2,1 occurs in the base 3 representation of n but not of n+1.

7, 16, 23, 25, 34, 43, 50, 52, 61, 71, 77, 79, 88, 97, 104, 106, 115, 124, 131, 133, 142, 152, 158, 160, 169, 178, 185, 187, 215, 223, 233, 239, 241, 250, 259, 266, 268, 277, 286, 293, 295, 304, 314, 320, 322, 331, 340, 347, 349