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 A052756 #23 Nov 05 2017 23:06:23
%S A052756 0,1,6,81,1728,50625,1889568,85766121,4586471424,282429536481,
%T A052756 19683000000000,1531578985264449,131621703842267136,
%U A052756 12381557655576425121,1265437718438866624512,139628860198736572265625,16543163447903718821855232,2094704750199298376445300801
%N A052756 E.g.f.: (-1/3)*LambertW(-3*x).
%C A052756 Previous name was: A simple grammar.
%H A052756 G. C. Greubel, <a href="/A052756/b052756.txt">Table of n, a(n) for n = 0..330</a>
%H A052756 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=712">Encyclopedia of Combinatorial Structures 712</a>
%F A052756 E.g.f.: (-1/3)*LambertW(-3*x).
%F A052756 For n>0, a(n) = (3*n)^(n-1). - _Vaclav Kotesovec_, Sep 30 2013
%F A052756 a(n) = [x^n] x/(1 - 3*n*x). - _Ilya Gutkovskiy_, Oct 12 2017
%p A052756 spec := [S,{S=Prod(B,B,B,Z),B=Set(S)},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t A052756 With[{nn=20},CoefficientList[Series[-1/3 LambertW[-3x],{x,0,nn}],x] Range[0,nn]!] (* _Harvey P. Dale_, Jun 01 2013 *)
%o A052756 (PARI) x='x+O('x^50); concat([0], Vec(serlaplace((-1/3)*lambertw(-3*x)))) \\ _G. C. Greubel_, Nov 05 2017
%K A052756 easy,nonn
%O A052756 0,3
%A A052756 encyclopedia(AT)pommard.inria.fr, Jan 25 2000
%E A052756 New name using e.g.f. by _Vaclav Kotesovec_, Sep 30 2013