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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
OFFSET
0,3
LINKS
FORMULA
a(n) = A088326(2n,n) = A088326(2n+k,n+k) for k >= 0.
CROSSREFS
Cf. A088326.
Sequence in context: A034740 A367293 A323936 * A322110 A375617 A232973
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jun 11 2018
STATUS
approved