

A151880


Triangle: R*(n,k) (n>=2, k from 2 to n1 or to 2 if n = 2), where R*(n,k) = number of trees with n nodes and k unlabeled endnodes.


2



1, 1, 1, 1, 1, 2, 3, 1, 3, 9, 12, 1, 4, 18, 52, 60, 1, 5, 30, 136, 360, 360
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OFFSET

0,6


COMMENTS

All nodes are labeled except for the endnodes.


LINKS



FORMULA

There is an explicit formula in terms of Stirling numbers of the second kind.


EXAMPLE

Triangle (in fact the columns in the original have been reversed and the triangle transposed):
(n=2) 1
(n=3) 1
(n=4) 1 1
(n=5) 1 2 3
(n=6) 1 3 9 12
(n=7) 1 4 18 52 60
(n=8) 1 5 30 136 360 360


CROSSREFS

See A213262 for a better version with more terms and a program.


KEYWORD

nonn,tabf


AUTHOR



STATUS

approved



