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%I #7 Jul 04 2017 13:18:31
%S 26,126,226,269,326,426,526,626,726,826,926,1026,1126,1226,1269,1326,
%T 1426,1526,1626,1726,1826,1926,2026,2126,2226,2269,2326,2426,2526,
%U 2699,2726,2826,2926,3026,3126,3226,3269,3326,3426
%N Numbers n such that string 2,6 occurs in the base 10 representation of n but not of n+1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{2,6}]>0,1,0],{n,3500}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jul 04 2017 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_