%I #7 Oct 08 2020 16:00:53
%S 18,99,170,180,261,342,423,504,585,666,747,828,899,909,990,1071,1152,
%T 1233,1314,1395,1538,1557,1628,1638,1719,1800,1881,1962,2043,2124,
%U 2205,2286,2357,2367,2448,2529,2610,2691,2772,2853
%N Numbers n such that string 2,0 occurs in the base 9 representation of n but not of n+1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,9],{2,0}]>0,1,0],{n,3000}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Oct 08 2020 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_