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 A113727 #8 Jun 13 2015 00:51:54
%S A113727 1,0,4,4,17,32,88,200,497,1184,2876,6924,16737,40384,97520,235408,
%T A113727 568353,1372096,3312564,7997204,19306993,46611168,112529352,271669848,
%U A113727 655869073,1583407968,3822685036,9228778012,22280241089,53789260160
%N A113727 A Pell convolution.
%C A113727 Convolution of A000129(n+1) and (n+1)*(-1)^n.
%H A113727 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,4,1).
%F A113727 G.f.: 1/((1-2x-x^2)(1+2x+x^2)); a(n)=4a(n-2)+4a(n-3)+a(n-4); a(n)=sum{k=0..floor(n/2), C(n-k, k)2^(n-2k)*(1+(-1)^(n-k))/2}.
%F A113727 a(n) = A000129(n+1)/2 +(n+1)*(-1)^n/2. - _R. J. Mathar_, Sep 20 2012
%t A113727 LinearRecurrence[{0,4,4,1},{1,0,4,4},30] (* _Harvey P. Dale_, May 24 2014 *)
%Y A113727 Cf. A094686, A113726.
%K A113727 easy,nonn
%O A113727 0,3
%A A113727 _Paul Barry_, Nov 08 2005