A185650 a(n) is the number of rooted trees with 2n vertices n of whom are leaves.
1, 2, 8, 39, 214, 1268, 7949, 51901, 349703, 2415348, 17020341, 121939535, 885841162, 6511874216, 48359860685, 362343773669, 2736184763500, 20805175635077, 159174733727167, 1224557214545788, 9467861087020239, 73534456468877012, 573484090227222260
Offset: 1
Keywords
Examples
From _Gus Wiseman_, Nov 27 2022: (Start) The a(1) = 1 through a(3) = 8 rooted trees: (o) ((oo)) (((ooo))) (o(o)) ((o)(oo)) ((o(oo))) ((oo(o))) (o((oo))) (o(o)(o)) (o(o(o))) (oo((o))) (End)
Links
- Andrew Howroyd, Table of n, a(n) for n = 1..200
- V. M. Kharlamov and S. Yu. Orevkov, The number of trees half of whose vertices are leaves and asymptotic enumeration of plane real algebraic curves, arXiv:math/0301245 [math.AG], 2003; J. of Combinatorial Theory, Ser. A, 105 (2004), 127-142.
- Index entries for sequences related to rooted trees
Crossrefs
Programs
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Mathematica
terms = 23; m = 2 terms; T[, ] = 0; Do[T[x_, z_] = z x - x + x Exp[Sum[Series[1/k T[x^k, z^k], {x, 0, j}, {z, 0, j}], {k, 1, j}]] // Normal, {j, 1, m}]; cc = CoefficientList[#, z]& /@ CoefficientList[T[x, z] , x]; Table[cc[[2n+1, n+1]], {n, 1, terms}] (* Jean-François Alcover, Sep 14 2018 *) art[n_]:=If[n==1,{{}},Join@@Table[Select[Tuples[art/@c],OrderedQ],{c,Join@@Permutations/@IntegerPartitions[n-1]}]]; Table[Length[Select[art[n],Count[#,{},{-2}]==n/2&]],{n,2,10,2}] (* Gus Wiseman, Nov 27 2022 *)
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PARI
\\ here R is A055277 as vector of polynomials R(n) = {my(A = O(x)); for(j=1, n, A = x*(y - 1 + exp( sum(i=1, j, 1/i * subst( subst( A + x * O(x^(j\i)), x, x^i), y, y^i) ) ))); Vec(A)}; {my(A=R(2*30)); vector(#A\2, k, polcoeff(A[2*k],k))} \\ Andrew Howroyd, May 21 2018
Extensions
Terms a(20) and beyond from Andrew Howroyd, May 21 2018
Comments