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Numbers n such that string 8,1 occurs in the base 9 representation of n but not of n-1.
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%I #7 Dec 18 2018 13:58:00

%S 73,154,235,316,397,478,559,640,657,721,802,883,964,1045,1126,1207,

%T 1288,1369,1386,1450,1531,1612,1693,1774,1855,1936,2017,2098,2115,

%U 2179,2260,2341,2422,2503,2584,2665,2746,2827,2844

%N Numbers n such that string 8,1 occurs in the base 9 representation of n but not of n-1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,9],{8,1}]>0,1,0],{n,3000}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Dec 18 2018 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_