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A052665 a(0)=0, for n >= 1, a(n) = ((2^(n-1)-1)*n!. 0
0, 0, 2, 18, 168, 1800, 22320, 317520, 5120640, 92534400, 1854316800, 40834886400, 980516275200, 25499650176000, 714077383219200, 21423629170944000, 685577056260096000, 23309975600271360000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..17.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 612

FORMULA

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

Recurrence: {a(1)=0, a(0)=0, a(2)=2, (2*n^2+6*n+4)*a(n)+(-6-3*n)*a(n+1)+a(n+2)}

MAPLE

spec := [S, {S=Prod(Z, Z, Sequence(Z), Sequence(Union(Z, Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);

CROSSREFS

Sequence in context: A037623 A052865 A052883 * A259880 A092473 A318218

Adjacent sequences:  A052662 A052663 A052664 * A052666 A052667 A052668

KEYWORD

easy,nonn

AUTHOR

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

STATUS

approved

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Last modified July 5 04:19 EDT 2020. Contains 335459 sequences. (Running on oeis4.)