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 A052639 #13 Apr 18 2017 07:03:58
%S A052639 1,0,0,6,48,480,6480,100800,1774080,35199360,776563200,18840729600,
%T A052639 498640665600,14297239756800,441470866636800,14605415016192000,
%U A052639 515412006100992000,19325209343311872000,767215648278503424000
%N A052639 E.g.f. (1-2x)/(1-2x-x^3).
%H A052639 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=585">Encyclopedia of Combinatorial Structures 585</a>
%F A052639 E.g.f.: (-1+2*x)/(-1+2*x+x^3)
%F A052639 Recurrence: {a(1)=0, a(0)=1, a(2)=0, (-11*n-6-n^3-6*n^2)*a(n)+(-2*n-6)*a(n+2)+a(n+3)=0}
%F A052639 Sum(-1/59*(8+6*_alpha^2-25*_alpha)*_alpha^(-1-n), _alpha=RootOf(-1+2*_Z+_Z^3))*n!
%F A052639 a(n)= n!*A008998(n-3), n>2. - _R. J. Mathar_, Nov 27 2011
%p A052639 spec := [S,{S=Sequence(Prod(Z,Z,Z,Sequence(Union(Z,Z))))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K A052639 easy,nonn
%O A052639 0,4
%A A052639 encyclopedia(AT)pommard.inria.fr, Jan 25 2000