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 A112518 #15 Jun 08 2024 04:13:19
%S A112518 1,1,1,-1,-4,-7,-6,3,21,40,40,-5,-106,-226,-256,-39,519,1257,1591,592,
%T A112518 -2441,-6880,-9655,-5365,10836,37026,57411,41104,-43784,-195632,
%U A112518 -335251,-288787,146261,1012395,1925220,1921485,-249566,-5112401,-10880591,-12302944
%N A112518 Expansion of g.f. 1/(1 - x + 2*x^3 + x^4).
%H A112518 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,-2,-1).
%F A112518 a(n) = a(n-1) - 2*a(n-3) - a(n-4).
%F A112518 a(n) = Sum_{k=0..n} Sum_{j=0..n} C(j, n-j)*C(k, j-k)*(-1)^(j-k).
%t A112518 LinearRecurrence[{1,0,-2,-1},{1,1,1,-1},40] (* _James C. McMahon_, Jun 07 2024 *)
%Y A112518 Row sums of A112517.
%K A112518 easy,sign
%O A112518 0,5
%A A112518 _Paul Barry_, Sep 09 2005