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%I #10 Aug 23 2021 21:47:10
%S 47,74,147,174,247,274,347,374,447,470,547,574,647,674,740,774,847,
%T 874,947,974,1047,1074,1147,1174,1247,1274,1347,1374,1447,1470,1547,
%U 1574,1647,1674,1740,1774,1847,1874,1947,1974,2047
%N Numbers k such that 4 and 7 occur juxtaposed in the base-10 representation of k but not of k-1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{4,7}]>0 || SequenceCount[ IntegerDigits[n],{7,4}]>0,1,0],{n,2100}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jun 20 2019 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_
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