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%I #13 Aug 28 2021 02:51:04
%S 13,31,113,139,213,231,319,331,413,431,513,531,613,631,713,731,813,
%T 831,913,931,1013,1031,1113,1139,1213,1231,1399,1413,1431,1513,1531,
%U 1613,1631,1713,1731,1813,1831,1913,1931,2013,2031
%N Numbers k such that 1 and 3 occur juxtaposed in the base-10 representation of k but not of k+1.
%H Michael De Vlieger, <a href="/A044006/b044006.txt">Table of n, a(n) for n = 1..10000</a>
%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{1,3}]>0 || SequenceCount[ IntegerDigits[n],{3,1}]>0,1,0],{n,2100}],{1,0}][[All,1]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 18 2019 *)
%K nonn,base
%O 1,1
%A _Clark Kimberling_