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 A052730 #13 Jun 03 2022 18:16:52
%S A052730 0,0,0,6,72,1440,35280,1058400,37376640,1520830080,70053984000,
%T A052730 3603888288000,204806714112000,12742502111539200,861483843034214400,
%U A052730 62887137880799232000,4929809613351727104000,413044721987184967680000
%N A052730 A simple context-free grammar in a labeled universe.
%H A052730 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=686">Encyclopedia of Combinatorial Structures 686</a>
%F A052730 E.g.f.: RootOf(-_Z+_Z^2+_Z^3+x)-RootOf(-_Z+_Z^2+_Z^3+x)^2-x
%F A052730 D-finite Recurrence: {a(1)=0, a(2)=0, a(3)=6, a(4)=72, (-105*n+135*n^3+30)*a(n) +(-130-107*n+29*n^2)*a(n+1) +(-99-91*n)*a(n+2) +15*a(n+3)=0.
%F A052730 a(n) = n!*A052703(n). - _R. J. Mathar_, Oct 18 2013
%p A052730 spec := [S,{C=Prod(B,B),B=Union(S,Z,C),S=Prod(B,C)},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%K A052730 easy,nonn
%O A052730 0,4
%A A052730 encyclopedia(AT)pommard.inria.fr, Jan 25 2000