This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A044449 #7 Apr 19 2015 09:41:08
%S A044449 7,23,31,39,55,71,87,95,103,127,135,151,159,167,183,199,215,223,231,
%T A044449 247,263,279,287,295,311,327,343,351,359,383,391,407,415,423,439,511,
%U A044449 519,535,543,551,567,583,599,607,615,639,647,663
%N A044449 Numbers n such that string 1,3 occurs in the base 4 representation of n but not of n+1.
%H A044449 Harvey P. Dale, <a href="/A044449/b044449.txt">Table of n, a(n) for n = 1..1000</a>
%t A044449 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 A044449 nonn,base
%O A044449 1,1
%A A044449 _Clark Kimberling_