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 A110524 #13 Sep 08 2022 08:45:20
%S A110524 1,-1,2,-6,14,-32,76,-180,424,-1000,2360,-5568,13136,-30992,73120,
%T A110524 -172512,407008,-960256,2265536,-5345088,12610688,-29752448,70195072,
%U A110524 -165611520,390727936,-921846016,2174915072,-5131286016,12106264064,-28562358272,67387288576,-158987105280
%N A110524 Expansion of (1 + x)/(1 + 2*x + 2*x^3).
%C A110524 Diagonal sums of number triangle A110522.
%H A110524 G. C. Greubel, <a href="/A110524/b110524.txt">Table of n, a(n) for n = 0..1000</a>
%H A110524 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-2,0,-2)
%F A110524 a(n) = Sum_{k=0..floor(n/2)} Sum_{j=0..(n-k)} (-1)^(n-k-j)*C(n-k, j) *(-3)^(j-k)*C(k, j-k).
%F A110524 a(n) = (-1)^n * A077999(n). - _G. C. Greubel_, Jun 27 2019
%t A110524 CoefficientList[Series[(1+x)/(1+2*x+2*x^3), {x,0,40}], x] (* _G. C. Greubel_, Aug 30 2017 *)
%t A110524 LinearRecurrence[{-2,0,-2}, {1,-1,2}, 40] (* _G. C. Greubel_, Jun 27 2019 *)
%o A110524 (PARI) my(x='x+O('x^40)); Vec((1+x)/(1+2*x+2*x^3)) \\ _G. C. Greubel_, Aug 30 2017
%o A110524 (Magma) R<x>:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1+x)/( 1+2*x+2*x^3) )); // _G. C. Greubel_, Jun 27 2019
%o A110524 (Sage) ((1+x)/(1+2*x+2*x^3)).series(x, 40).coefficients(x, sparse=False) # _G. C. Greubel_, Jun 27 2019
%o A110524 (GAP) a:=[1,-1,2];; for n in [4..40] do a[n]:=-2*(a[n-1]+a[n-3]); od; a; # _G. C. Greubel_, Jun 27 2019
%Y A110524 Cf. A077999.
%K A110524 easy,sign
%O A110524 0,3
%A A110524 _Paul Barry_, Jul 24 2005