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A052711 E.g.f. x*(1-2*x-sqrt(1-4*x))/2. 1
0, 0, 0, 6, 48, 600, 10080, 211680, 5322240, 155675520, 5189184000, 194075481600, 8045310873600, 366061644748800, 18134130709094400, 971471287987200000, 55956746188062720000, 3448334483839365120000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 667

FORMULA

Recurrence: a(1)=0; a(2)=0; a(3)=6; a(4)=48; (2*n+6-4*n^2)*a(n)+a(n+1)*n =0.

a(n) = n!*A000108(n-2). a(n) = A052717(n), n>2. - R. J. Mathar, Oct 18 2013

MAPLE

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

MATHEMATICA

With[{nn=20}, CoefficientList[Series[x (1-2x-Sqrt[1-4x])/2, {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Mar 05 2016 *)

CROSSREFS

Sequence in context: A209670 A223270 A052731 * A113388 A113393 A138426

Adjacent sequences:  A052708 A052709 A052710 * A052712 A052713 A052714

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified February 21 15:34 EST 2019. Contains 320374 sequences. (Running on oeis4.)