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%I #7 Jan 23 2021 12:31:37
%S 17,117,170,217,317,417,517,617,717,817,917,1017,1117,1170,1217,1317,
%T 1417,1517,1617,1700,1817,1917,2017,2117,2170,2217,2317,2417,2517,
%U 2617,2717,2817,2917,3017,3117,3170,3217,3317,3417
%N Numbers n such that string 1,7 occurs in the base 10 representation of n but not of n-1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{1,7}]>0,1,0],{n,3500}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 23 2021 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_