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 A052620 #13 Jun 03 2022 18:51:32
%S A052620 1,1,8,66,768,11040,190800,3845520,88583040,2295578880,66098592000,
%T A052620 2093556326400,72337863628800,2707751497651200,109153235884492800,
%U A052620 4714413247095552000,217193790828478464000,10631538129843671040000
%N A052620 E.g.f. (1-x)^2/(1-3x+x^3).
%H A052620 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=566">Encyclopedia of Combinatorial Structures 566</a>
%F A052620 E.g.f.: (-1+x)^2/(1-3*x+x^3)
%F A052620 Recurrence: {a(1)=1, a(0)=1, a(2)=8, (n^3+6*n^2+11*n+6)*a(n) +(-3*n-9)*a(n+2) +a(n+3)=0}
%F A052620 Sum(-1/9*(-1+2*_alpha^2-2*_alpha)*_alpha^(-1-n), _alpha=RootOf(1-3*_Z+_Z^3))*n!
%F A052620 a(n) = n!*A052545(n). - _R. J. Mathar_, Jun 03 2022
%p A052620 spec := [S,{S=Sequence(Prod(Z,Sequence(Z),Union(Z,Sequence(Z))))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K A052620 easy,nonn
%O A052620 0,3
%A A052620 encyclopedia(AT)pommard.inria.fr, Jan 25 2000