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 A052599 #18 Apr 10 2022 14:24:50
%S A052599 1,2,8,54,480,5280,69840,1078560,19031040,377758080,8331724800,
%T A052599 202138675200,5349968870400,153396430387200,4736570917478400,
%U A052599 156702542540544000,5529893367398400000,207341583834857472000
%N A052599 Expansion of e.g.f.: 1/(1-2x-x^3).
%H A052599 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=544">Encyclopedia of Combinatorial Structures 544</a>
%F A052599 E.g.f.: -1/(-1+2*x+x^3)
%F A052599 Recurrence: {a(0)=1, a(1)=2, a(2)=8, (-11*n-6-n^3-6*n^2)*a(n) +(-2*n-6)*a(n+2) +a(n+3)=0}
%F A052599 Sum(1/59*(16+12*_alpha^2+9*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^3))*n!
%F A052599 a(n) = n!*A008998(n). - _R. J. Mathar_, Nov 27 2011
%p A052599 spec := [S,{S=Sequence(Union(Z,Z,Prod(Z,Z,Z)))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t A052599 With[{nn=20},CoefficientList[Series[1/(1-2x-x^3),{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Apr 10 2022 *)
%K A052599 easy,nonn
%O A052599 0,2
%A A052599 encyclopedia(AT)pommard.inria.fr, Jan 25 2000
%E A052599 Definition clarified by _Harvey P. Dale_, Apr 10 2022