A291952 Number of ordered pairs of edge-disjoint trees on n labeled vertices.

1, 0, 0, 12, 1140, 147240, 27351240, 7080803520, 2459711381904, 1109036355638400, 631326674047988160, 443473982265049781760, 377141923845397281954240, 382112718284033118371877888, 454983035518312016029934256000

Offset

1,4

Links

Table of n, a(n) for n=1..15.

J. W. Moon, The second moment of the complexity of a graph, Mathematika 11:2 (1964), 95-98.

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

Adjacent sequences: A291949 A291950 A291951 * A291953 A291954 A291955

Keyword

nonn

Author

Max Alekseyev, Sep 06 2017

Status

approved