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A291952
Number of ordered pairs of edge-disjoint trees on n labeled vertices.
2
1, 0, 0, 12, 1140, 147240, 27351240, 7080803520, 2459711381904, 1109036355638400, 631326674047988160, 443473982265049781760, 377141923845397281954240, 382112718284033118371877888, 454983035518312016029934256000
OFFSET
1,4
LINKS
FORMULA
a(n) = Sum_{m=0..n-1} (-1)^m * n^(2*(n-m-2)) * (n-1)!/(n-1-m)! * Sum_{t=0..m} binomial(n-t,m-t) * n^t/t!.
PROG
(PARI) { A291952(n) = sum(m=0, n-1, (-1)^m * n^(2*(n-m-2)) * (n-1)!/(n-1-m)! * sum(t=0, m, binomial(n-t, m-t) * n^t/t!) ); }
CROSSREFS
Cf. A291953.
Sequence in context: A109229 A112457 A091782 * A112580 A229691 A180586
KEYWORD
nonn
AUTHOR
Max Alekseyev, Sep 06 2017
STATUS
approved