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Numbers n such that string 1,1 occurs in the base 10 representation of n but not of n-1.
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%I #7 Aug 05 2019 13:13:12

%S 11,110,211,311,411,511,611,711,811,911,1011,1100,1211,1311,1411,1511,

%T 1611,1711,1811,1911,2011,2110,2211,2311,2411,2511,2611,2711,2811,

%U 2911,3011,3110,3211,3311,3411,3511,3611,3711,3811

%N Numbers n such that string 1,1 occurs in the base 10 representation of n but not of n-1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{1,1}]>0,1,0],{n,4000}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 05 2019 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_