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A245855 Number of preferential arrangements of n labeled elements such that the minimal number of elements per rank equals 2. 2
1, 0, 6, 20, 120, 672, 5516, 40140, 368640, 3521870, 37445298, 422339502, 5215454426, 68144100780, 954428684280, 14160968076584, 222769496190060, 3692874342747114, 64493471050666430, 1181830474135532130, 22692074431844298558, 455404848204906308984 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,3

LINKS

Alois P. Heinz, Table of n, a(n) for n = 2..400

FORMULA

E.g.f.: 1/(2-exp(x)+x) -1/(2-exp(x)+x+x^2/2).

a(n) = A032032(n) - A102233(n) = A245732(n,2) - A245732(n,3).

MAPLE

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

add(b(n-j, k)*binomial(n, j), j=k..n))

end:

a:= n-> b(n, 2) -b(n, 3):

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

CROSSREFS

Column k=2 of A245733.

Cf. A032032, A102233, A245732.

Sequence in context: A267855 A099840 A223045 * A074012 A074013 A333896

Adjacent sequences: A245852 A245853 A245854 * A245856 A245857 A245858

KEYWORD

nonn

AUTHOR

Alois P. Heinz, Aug 04 2014

STATUS

approved

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Last modified January 30 05:55 EST 2023. Contains 359939 sequences. (Running on oeis4.)