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 A113684 #6 Jun 13 2015 00:51:54
%S A113684 0,1,4,11,25,52,102,193,356,645,1153,2040,3580,6241,10820,18671,32089,
%T A113684 54956,93826,159745,271300,459721,777409,1312176,2211000,3719617,
%U A113684 6248452,10482323,17562841,29391460,49132638,82048705,136884260
%N A113684 Expansion of x(1-x^2-x^3)/((1-x)(1-x-x^2))^2.
%H A113684 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4,-2,4,0,-1)
%F A113684 a(n)=4a(n-1)-4a(n-2)-2a(n-3)+4a(n-4)-a(n-6); a(n)=sum{k=0..n, (n-k)*C(n-k, k+1)}; a(n)=n*(F(n+2)-1)-(1+((n-5)*F(n-1)+(3n-8)*F(n))/5).
%Y A113684 Cf. A045925, A006478, A023610.
%K A113684 easy,nonn
%O A113684 0,3
%A A113684 _Paul Barry_, Nov 05 2005