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A320758 Number of ordered set partitions of [n] where the maximal block size equals two. 2
1, 6, 42, 330, 2970, 30240, 345240, 4377240, 61122600, 933055200, 15470254800, 277005128400, 5329454130000, 109681187616000, 2404894892400000, 55977698400624000, 1378748676601296000, 35829233832135744000, 979763376201049440000, 28124715476056399200000 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,2

LINKS

Alois P. Heinz, Table of n, a(n) for n = 2..428

FORMULA

E.g.f.: 1/(1-Sum_{i=1..2} x^i/i!) - 1/(1-x).

A(n) = A080599(n) - A000142(n).

MAPLE

b:= proc(n, k) option remember; `if`(n=0, 1, add(

      b(n-i, k)*binomial(n, i), i=1..min(n, k)))

    end:

a:= n-> (k-> b(n, k) -b(n, k-1))(2):

seq(a(n), n=2..25);

CROSSREFS

Column k=2 of A276922.

Cf. A000142, A080599.

Sequence in context: A165314 A082302 A144223 * A262671 A029588 A001725

Adjacent sequences:  A320755 A320756 A320757 * A320759 A320760 A320761

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Oct 20 2018

STATUS

approved

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Last modified February 23 12:03 EST 2019. Contains 320431 sequences. (Running on oeis4.)