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 A179648 #18 Sep 08 2022 08:45:54
%S A179648 1,-3,12,-47,190,-778,3224,-13475,56710,-239986,1020200,-4353430,
%T A179648 18636908,-80004388,344264624,-1484499811,6413133638,-27750688914,
%U A179648 120258432264,-521833284514,2267084792708,-9859984425324,42925569027408
%N A179648 Expansion of (1/(1+4x-2x^2))*c(x/(1+4x-2x^2)), c(x) the g.f. of A000108.
%C A179648 Hankel transform is the (4,5) Somos-4 sequence A174404.
%H A179648 G. C. Greubel, <a href="/A179648/b179648.txt">Table of n, a(n) for n = 0..1540</a>
%F A179648 G.f.: (1/(2*x))*(1-sqrt((1-2*x^2)/(1+4*x-2*x^2))) = (sqrt(2*x^2-4*x-1)-sqrt(2*x^2-1))/(2*x*sqrt(2*x^2-4*x-1));
%F A179648 G.f.: 1/(1+4x-2x^2-x/(1-x/(1+4x-2x^2-x/(1-x/(1+4x-2x^2-x/(1-x/(1-... (continued fraction).
%F A179648 Conjecture: (n+1)*a(n) +2*(2n+1)*a(n-1) +4*(1-n)*a(n-2) +4*(5-2n)*a(n-3) +4*(n-3)*a(n-4)=0. - _R. J. Mathar_, Nov 17 2011
%F A179648 a(n) ~ (-1)^n * (2 + sqrt(6))^(n+1) / (2^(3/4) * 3^(1/4) * sqrt(Pi*n)). - _Vaclav Kotesovec_, Aug 15 2018
%t A179648 CoefficientList[Series[(1/(2*x))*(1 - Sqrt[(1-2*x^2)/(1+4*x-2*x^2)]), {x, 0, 50}], x] (* _G. C. Greubel_, Aug 14 2018 *)
%o A179648 (PARI) x='x+O('x^50); Vec((1/(2*x))*(1-sqrt((1-2*x^2)/(1+4*x-2*x^2)))) \\ _G. C. Greubel_, Aug 14 2018
%o A179648 (Magma) m:=50; R<x>:=PowerSeriesRing(Rationals(), m); Coefficients(R!((1/(2*x))*(1-Sqrt((1-2*x^2)/(1+4*x-2*x^2))))); // _G. C. Greubel_, Aug 14 2018
%Y A179648 Cf. A000108, A174404.
%K A179648 sign,easy
%O A179648 0,2
%A A179648 _Paul Barry_, Jan 09 2011