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 A117363 #6 Aug 04 2021 15:29:51
%S A117363 1,-2,1,-3,3,-4,6,-7,10,-13,17,-23,30,-40,53,-70,93,-123,163,-216,286,
%T A117363 -379,502,-665,881,-1167,1546,-2048,2713,-3594,4761,-6307,8355,-11068,
%U A117363 14662,-19423,25730,-34085,45153,-59815,79238
%N A117363 Expansion of (1-2x)/(1-x^2+x^3).
%C A117363 Diagonal sums of number triangle A117362.
%H A117363 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,-1).
%F A117363 a(n)=a(n-2)-a(n-3); a(n)=sum{k=0..floor(n/2), (-1)^n*(C(k,n-2k)+2*C(k,n-2k-1))}.
%t A117363 CoefficientList[Series[(1-2x)/(1-x^2+x^3),{x,0,60}],x] (* or *) LinearRecurrence[ {0,1,-1},{1,-2,1},60] (* _Harvey P. Dale_, Aug 04 2021 *)
%Y A117363 Cf. A109248, A007307.
%K A117363 easy,sign
%O A117363 0,2
%A A117363 _Paul Barry_, Mar 10 2006