A227806 Number of rooted identity trees with n nodes and exactly 2 subtrees from the root.

1, 1, 3, 5, 11, 22, 49, 104, 232, 513, 1159, 2619, 5989, 13734, 31729, 73555, 171377, 400631, 940104, 2212542, 5222932, 12360976, 29327260, 69735757, 166170966, 396727768, 948897250, 2273409345, 5455374972, 13110384631, 31550978034, 76029236983, 183437066950

Offset: 4

Author

Alois P. Heinz, Jul 31 2013

Keywords

• nonn

Examples

			:    o    :    o    :    o         o       o    :
:   / \   :   / \   :   / \       / \     / \   :
:  o   o  :  o   o  :  o   o     o   o   o   o  :
:  |      :  |      :  |   |    / \      |      :
:  o      :  o      :  o   o   o   o     o      :
:         :  |      :  |       |         |      :
:         :  o      :  o       o         o      :
:         :         :                    |      :
:  n=4    :  n=5    :  n=6               o      :
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 4..800

Crossrefs

Column k=2 of A227774.

Formula

a(n) ~ c * d^n / n^(3/2), where d = A246169 = 2.51754035263200389079535459846344... and c = 0.14400421547102520752812171064737721... - Vaclav Kotesovec, Jun 07 2021