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 A117374 #10 May 06 2022 14:54:47
%S A117374 1,-3,1,-4,4,-5,8,-9,13,-17,22,-30,39,-52,69,-91,121,-160,212,-281,
%T A117374 372,-493,653,-865,1146,-1518,2011,-2664,3529,-4675,6193,-8204,10868,
%U A117374 -14397,19072,-25265,33469
%N A117374 Expansion of (1-3x)/(1-x^2+x^3).
%C A117374 Diagonal sums of number triangle A117372.
%H A117374 Harvey P. Dale, <a href="/A117374/b117374.txt">Table of n, a(n) for n = 0..1000</a>
%H A117374 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,-1).
%F A117374 a(n)=a(n-2)+a(n-3); a(n)=sum{k=0..floor(n/2), (-1)^n*(C(k,n-2k)+3*C(k, n-2k-1))}.
%t A117374 CoefficientList[Series[(1-3x)/(1-x^2+x^3),{x,0,40}],x] (* or *) LinearRecurrence[{0,1,-1},{1,-3,1},40] (* _Harvey P. Dale_, May 06 2022 *)
%K A117374 easy,sign
%O A117374 0,2
%A A117374 _Paul Barry_, Mar 10 2006