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Numbers n such that string 1,3 occurs in the base 4 representation of n but not of n+1.
2

%I #7 Apr 19 2015 09:41:08

%S 7,23,31,39,55,71,87,95,103,127,135,151,159,167,183,199,215,223,231,

%T 247,263,279,287,295,311,327,343,351,359,383,391,407,415,423,439,511,

%U 519,535,543,551,567,583,599,607,615,639,647,663

%N Numbers n such that string 1,3 occurs in the base 4 representation of n but not of n+1.

%H Harvey P. Dale, <a href="/A044449/b044449.txt">Table of n, a(n) for n = 1..1000</a>

%t Transpose[SequencePosition[Table[If[SequenceCount[IntegerDigits[n,4],{1,3}]>0,1,0],{n,700}],{1,0}]][[1]] (* The program uses the SequencePosition and SequenceCount functions from Mathematica version 10 *) (* _Harvey P. Dale_, Apr 19 2015 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_