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%I #11 Sep 15 2019 08:49:31
%S 21,70,119,147,168,217,266,315,364,413,462,490,511,560,609,658,707,
%T 756,805,833,854,903,952,1001,1029,1099,1148,1176,1197,1246,1295,1344,
%U 1393,1442,1491,1519,1540,1589,1638,1687,1736,1785
%N Numbers n such that string 3,0 occurs in the base 7 representation of n but not of n-1.
%t Select[Range[2000],MemberQ[Partition[IntegerDigits[#,7],2,1],{3,0}] && !MemberQ[Partition[IntegerDigits[#-1,7],2,1],{3,0}]&] (* or *) Flatten[ Position[Partition[If[MemberQ[Partition[IntegerDigits[#,7],2,1],{3,0}],1,0]&/@Range[2000],2,1],{0,1}]]+1 (* _Harvey P. Dale_, Aug 21 2013 *)
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n,7],{3,0}]>0,1,0],{n,1800}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 15 2019 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_
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