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 A078484 #19 Oct 16 2017 13:00:28
%S A078484 0,1,2,6,18,52,148,420,1192,3384,9608,27280,77456,219920,624416,
%T A078484 1772896,5033760,14292288,40579904,115217984,327136896,928835456,
%U A078484 2637230208,7487852800,21260161280,60363694336,171389837824,486624896512,1381667623424,3922950583296
%N A078484 G.f.: -x*(1-2*x+2*x^2)/(2*x^3-4*x^2+4*x-1).
%C A078484 Enumerates pop-stacks.
%H A078484 Vincenzo Librandi, <a href="/A078484/b078484.txt">Table of n, a(n) for n = 0..1000</a>
%H A078484 M. D. Atkinson and T. Stitt, <a href="http://www.cs.otago.ac.nz/staffpriv/mike/Papers/WreathProduct/Wreathpaper.pdf">Restricted permutations and the wreath product</a>, Preprint, 2002.
%H A078484 M. D. Atkinson and T. Stitt, <a href="http://dx.doi.org/10.1016/S0012-365X(02)00443-0">Restricted permutations and the wreath product</a>, Discrete Math., 259 (2002), 19-36.
%H A078484 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4, -4, 2).
%F A078484 a(0)=0, a(1)=1, a(2)=2, a(3)=6, a(n) = 4*a(n-1)-4*a(n-2)+2*a(n-3). - _Harvey P. Dale_, Jul 21 2012
%t A078484 CoefficientList[Series[-x(1-2x+2x^2)/(2x^3-4x^2+4x-1),{x,0,30}],x] (* or *) Join[{0},LinearRecurrence[{4,-4,2},{1,2,6},30]] (* _Harvey P. Dale_, Jul 21 2012 *)
%K A078484 nonn
%O A078484 0,3
%A A078484 _N. J. A. Sloane_, Jan 04 2003
%E A078484 Replaced definition with g.f. given by Atkinson and Stitt (2002). - _N. J. A. Sloane_, May 24 2016