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A220824 Number of rooted gene trees with n leaves on the label set [4]. 2
4, 10, 60, 430, 3396, 28818, 256172, 2357138, 22253672, 214370398, 2098593628, 20817790876, 208801698676, 2113957366698, 21574762692484, 221729081428478, 2292720460828372, 23835381083324608, 248987501825970604, 2612160344953154508, 27510833867426222908 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..200

V. P. Johnson, Enumeration Results on Leaf Labeled Trees, Ph. D. Dissertation, Univ. Southern Calif., 2012.

MATHEMATICA

A[n_, k_] := A[n, k] = If[n < 2, k n, If[OddQ[n], 0, (# (1 - #)/2)&[A[n/2, k]]] + Sum[A[i, k] A[n - i, k], {i, 1, n/2}]];

T[n_, k_] := Sum[(-1)^i Binomial[k, i] A[n, k - i], {i, 0, k}];

a[n_] := T[n, 5];

Array[a, 22] (* Jean-Fran├žois Alcover, Sep 02 2019, after Alois P. Heinz in A319254 *)

CROSSREFS

Column 4 of A319254.

Sequence in context: A222675 A328155 A209030 * A124724 A323870 A298162

Adjacent sequences:  A220821 A220822 A220823 * A220825 A220826 A220827

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 22 2012

EXTENSIONS

Terms a(11) and beyond from Andrew Howroyd, Sep 17 2018

STATUS

approved

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Last modified October 24 20:35 EDT 2021. Contains 348233 sequences. (Running on oeis4.)