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 A054366 #24 May 02 2018 22:34:29
%S A054366 1,1,6,21,146,1101,10632,107062,1151802,12845442,147845706,1743640908,
%T A054366 20988257544,256987965379,3192893716320,40171643847696,
%U A054366 510997002280522,6563060603543658,85017387536789916,1109744672540225367,14585261039005676046
%N A054366 Number of unlabeled 6-ary cacti having n polygons.
%H A054366 Andrew Howroyd, <a href="/A054366/b054366.txt">Table of n, a(n) for n = 0..200</a>
%H A054366 Miklos Bona, Michel Bousquet, Gilbert Labelle and Pierre Leroux, <a href="http://dx.doi.org/10.1006/aama.1999.0665">Enumeration of m-ary cacti</a>, Advances in Applied Mathematics, 24 (2000), 22-56.
%H A054366 <a href="/index/Ca#cacti">Index entries for sequences related to cacti</a>
%F A054366 a(n) = (1/n)*(Sum_{d|n} phi(n/d)*binomial(6*d, d)) - 5*binomial(6*n, n)/(5*n+1) for n > 0. - _Andrew Howroyd_, May 02 2018
%F A054366 a(n) ~ sqrt(3) * 6^(6*n) / (sqrt(Pi) * n^(5/2) * 5^(5*n + 3/2)). - _Vaclav Kotesovec_, Jul 17 2017
%t A054366 a[n_] := If[n == 0, 1, (Binomial[6*n, n]/(5 n + 1) + DivisorSum[n, Binomial[6*#, #]*EulerPhi[n/#]*Boole[# < n] & ])/n]; Table[a[n], {n, 0, 20}] (* _Jean-François Alcover_, Jul 17 2017 *)
%o A054366 (PARI) a(n) = if(n==0, 1, sumdiv(n, d, eulerphi(n/d)*binomial(6*d, d))/n - 5*binomial(6*n, n)/(5*n+1)) \\ _Andrew Howroyd_, May 02 2018
%Y A054366 Column k=6 of A303912.
%Y A054366 Cf. A054367, A054368.
%K A054366 nonn
%O A054366 0,3
%A A054366 _Simon Plouffe_
%E A054366 More terms from _Jean-François Alcover_, Jul 17 2017