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 A006964 M2994 #56 Jan 23 2019 02:33:05
%S A006964 1,3,15,82,495,3144,20875,142773,1000131,7136812,51702231,379234623,
%T A006964 2810874950,21020047557,158398829121,1201617201230,9169060501023,
%U A006964 70329406653879,541949364313821,4193569906262874,32571403998781956,253842927519362734,1984442128649393178
%N A006964 Number of directed rooted trees with n nodes.
%C A006964 Also rooted trees with n nodes and 3-colored non-root nodes. - _Christian G. Bower_, Apr 15 1998
%D A006964 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A006964 Alois P. Heinz, <a href="/A006964/b006964.txt">Table of n, a(n) for n = 1..500</a>
%H A006964 Loïc Foissy, <a href="https://arxiv.org/abs/1811.07572">Algebraic structures on typed decorated rooted trees</a>, arXiv:1811.07572 [math.RA], 2018.
%H A006964 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=439">Encyclopedia of Combinatorial Structures 439</a>
%H A006964 P. Leroux and B. Miloudi, <a href="http://www.labmath.uqam.ca/~annales/volumes/16-1/PDF/053-080.pdf">Généralisations de la formule d'Otter</a>, Ann. Sci. Mathh
%H A006964 . Québec, Vol. 16, No. 1 (1992) pp. 53-80.
%H A006964 P. Leroux and B. Miloudi, <a href="/A000081/a000081_2.pdf">Généralisations de la formule d'Otter</a>, Ann. Sci. Math. Québec, Vol. 16, No. 1, pp. 53-80, 1992. (Annotated scanned copy)
%H A006964 R. J. Mathar, <a href="http://arxiv.org/abs/1603.00077">Topologically Distinct Sets of Non-intersecting Circles in the Plane</a>, arXiv:1603.00077 [math.CO], 2016.
%H A006964 <a href="/index/Ro#rooted">Index entries for sequences related to rooted trees</a>
%H A006964 <a href="/index/Tra#trees">Index entries for sequences related to trees</a>
%F A006964 a(n+1) has g.f.: Product_{n>=1} (1 - x^3*a(n))^-1.
%F A006964 a(n) ~ c * d^n / n^(3/2), where d = 8.356026879295995368276069578708912..., c = 0.13645899548680457355557420025756... . - _Vaclav Kotesovec_, Aug 20 2014
%F A006964 G.f. A(x) satisfies: A(x) = x*exp(3*Sum_{k>=1} A(x^k)/k). - _Ilya Gutkovskiy_, Mar 19 2018
%p A006964 with(numtheory): a:= proc(n) option remember; `if`(n<2, n, (add(add(d*a(d), d=divisors(j)) *a(n-j)*3, j=1..n-1))/(n-1)) end: seq(a(n), n=1..30); # _Alois P. Heinz_, Sep 06 2008
%t A006964 a[n_] := a[n] = If[n<2, n, (Sum[Sum[d*a[d], {d, Divisors[j]}]*a[n-j]*3, {j, 1, n-1}])/(n-1)]; Table[a[n], {n, 1, 30}] (* _Jean-François Alcover_, Mar 30 2015, after _Alois P. Heinz_ *)
%Y A006964 Cf. A038059.
%Y A006964 Column k=3 of A242249.
%K A006964 nonn,eigen
%O A006964 1,2
%A A006964 _Simon Plouffe_
%E A006964 Extended by _Christian G. Bower_, Apr 15 1998