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%I #10 Aug 23 2021 21:46:52
%S 39,93,139,193,239,293,339,390,439,493,539,593,639,693,739,793,839,
%T 893,930,993,1039,1093,1139,1193,1239,1293,1339,1390,1439,1493,1539,
%U 1593,1639,1693,1739,1793,1839,1893,1930,1993,2039
%N Numbers k such that 3 and 9 occur juxtaposed in the base-10 representation of k but not of k-1.
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{3,9}]>0 || SequenceCount[ IntegerDigits[n],{9,3}]>0,1,0],{n,2100}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 22 2020 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_
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