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 A107443 #18 Mar 24 2024 12:42:19
%S A107443 1,1,1,1,-3,-3,9,9,-11,-11,1,1,45,45,-135,-135,229,229,-143,-143,-483,
%T A107443 -483,2025,2025,-4139,-4139,4321,4321,3597,3597,-28071,-28071,69829,
%U A107443 69829,-97199,-97199,12285,12285,351945,351945,-1104971,-1104971,1907137,1907137,-1301523,-1301523,-3723975,-3723975
%N A107443 Expansion of g.f.: (1+3*x^2)/((1-x)*(1+x+2*x^2)*(1-x+2*x^2)).
%H A107443 G. C. Greubel, <a href="/A107443/b107443.txt">Table of n, a(n) for n = 0..1000</a>
%H A107443 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,-3,3,-4,4).
%F A107443 a(2n) = a(2n+1) = A174565(n).
%F A107443 a(n) = (1 - 2*(-1)^n*A001607(n) + A001607(n+1))/2. - _G. C. Greubel_, Mar 24 2024
%p A107443 with(gfun): seriestolist(series((3*x^2+1)/((1-x)*(2*x^2+x+1)*(2*x^2-x+1)), x=0,50));
%t A107443 CoefficientList[Series[(1+3*x^2)/((1-x)*(1+3*x^2+4*x^4)), {x,0,50}], x] (* _G. C. Greubel_, Mar 24 2024 *)
%o A107443 (Magma) R<x>:=PowerSeriesRing(Integers(), 50); Coefficients(R!( (1+3*x^2)/((1-x)*(1+3*x^2+4*x^4)) )); // _G. C. Greubel_, Mar 24 2024
%o A107443 (SageMath)
%o A107443 def A107443_list(prec):
%o A107443 P.<x> = PowerSeriesRing(ZZ, prec)
%o A107443 return P( (1+3*x^2)/((1-x)*(1+3*x^2+4*x^4)) ).list()
%o A107443 A107443_list(50) # _G. C. Greubel_, Mar 24 2024
%Y A107443 Cf. A001607, A174565.
%K A107443 easy,sign
%O A107443 0,5
%A A107443 _Creighton Dement_, May 26 2005