%I #7 Jan 28 2020 14:08:55
%S 5,14,23,32,41,59,68,77,86,95,104,113,122,167,176,185,194,203,221,230,
%T 239,248,257,266,275,284,302,311,320,329,338,347,356,365,491,500,509,
%U 518,527,545,554,563,572,581,590,599,608,653
%N Numbers n such that string 1,2 occurs in the base 3 representation of n but not of n-1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,3],{1,2}]>0,1,0],{n,700}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 28 2020 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_