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A305839 Number of unlabeled forests of rooted trees with 2n edges and n connected components, in which the outdegree of each node is <= 2 and the symmetric group acts on the components. 2
1, 1, 3, 6, 15, 32, 77, 172, 405, 930, 2180, 5070, 11914, 27929, 65829, 155202, 367053, 868990, 2061723, 4897502, 11652547, 27757960, 66210042, 158103242, 377957299, 904439542, 2166408422, 5193894809, 12463003846, 29929966312, 71933014935, 173009938416 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..400

FORMULA

a(n) = A088326(2n,n) = A088326(2n+k,n+k) for k >= 0.

CROSSREFS

Cf. A088326.

Sequence in context: A316219 A034740 A323936 * A322110 A232973 A289006

Adjacent sequences:  A305836 A305837 A305838 * A305840 A305841 A305842

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Jun 11 2018

STATUS

approved

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Last modified April 7 04:20 EDT 2020. Contains 333292 sequences. (Running on oeis4.)