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 A061703 #9 Jun 13 2015 00:50:28 %S A061703 0,4,12,34,108,344,1104,3546,11396,36628,117732,378426,1216380, %T A061703 3909832,12567448,40395794,129844996,417363332,1341539196,4312135922, %U A061703 13860583628,44552347608,143205490528,460308235562,1479577849604 %N A061703 G.f.: 2*x*(2-2*x-3*x^2+2*x^3)/((1-3*x-x^2+x^3)*(1-x)). %D A061703 R. P. Stanley, Enumerative Combinatorics I, Example 4.7.17. %H A061703 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (4,-2,-2,1) %Y A061703 Row sums of A061702, A000183. %K A061703 easy,nonn %O A061703 0,2 %A A061703 _Vladeta Jovovic_, Jun 18 2001