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 A098580 #16 Sep 08 2022 08:45:15
%S A098580 1,-4,-16,-96,-640,-4480,-32256,-236544,-1757184,-13178880,-99573760,
%T A098580 -756760576,-5778898944,-44304891904,-340806860800,-2629081497600,
%U A098580 -20331563581440,-157569617756160,-1223481737871360,-9515969072332800,-74124390668697600
%N A098580 Expansion of (sqrt(1-8*x)-4*x)/sqrt(1-8*x).
%H A098580 G. C. Greubel, <a href="/A098580/b098580.txt">Table of n, a(n) for n = 0..1000</a>
%F A098580 G.f.: 1-4*x/sqrt(1-8*x).
%F A098580 a(0)=1, a(n) = -2^(n+1)*(2*(n-1))!/(n-1)!^2.
%F A098580 D-finite with recurrence: (n-1)*a(n) +4*(3-2*n)*a(n-1)=0. - _R. J. Mathar_, Sep 26 2012
%t A098580 CoefficientList[Series[(Sqrt[1-8x]-4x)/Sqrt[1-8x],{x,0,20}],x] (* _Harvey P. Dale_, May 06 2017 *)
%o A098580 (PARI) x='x+O('x^30); Vec((sqrt(1-8*x)-4*x)/sqrt(1-8*x)) \\ _G. C. Greubel_, Feb 03 2018
%o A098580 (Magma) Q:=Rationals(); R<x>:=PowerSeriesRing(Q, 40); Coefficients(R!((sqrt(1-8*x)-4*x)/sqrt(1-8*x))) // _G. C. Greubel_, Feb 03 2018
%Y A098580 Cf. A059304.
%K A098580 easy,sign
%O A098580 0,2
%A A098580 _Paul Barry_, Sep 16 2004