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 A099561 #5 Jun 13 2015 00:51:34 %S A099561 0,0,0,0,1,1,1,1,3,4,5,6,10,14,19,25,36,50,69,94,131,181,250,344,476, %T A099561 657,907,1251,1728,2385,3292,4543,6272,8657,11949,16492,22765,31422, %U A099561 43371,59863,82629,114051,157422,217285,299915,413966,571388,788673 %N A099561 Sum C(n-3k,k-1), k=0..floor(n/4). %H A099561 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,0,2,-1,0,0,-1). %F A099561 G.f.: x^4/((1-x^4)(1-x-x^4)); a(n)=a(n-1)+2a(n-4)-a(n-5)-a(n-8). %Y A099561 Cf. A074331, A099560, A099562. %K A099561 easy,nonn %O A099561 0,9 %A A099561 _Paul Barry_, Oct 22 2004