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A052713 E.g.f. (1-sqrt(1-8*x))/2. 0
0, 2, 8, 96, 1920, 53760, 1935360, 85155840, 4428103680, 265686220800, 18066663014400, 1373066389094400, 115337576683929600, 10611057054921523200, 1061105705492152320000, 114599416193152450560000 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Has a square root singularity.

LINKS

Table of n, a(n) for n=0..15.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 669

FORMULA

Recurrence: a(1)=2; (4-8*n)*a(n)+a(n+1) =0.

a(n+1) = 1/4*8^(n+1)*GAMMA(n+1/2)/Pi^(1/2)

a(n+1) = ((2*n)!/n!)*2^(n+1). - Zerinvary Lajos, Sep 25 2006

a(n) = n!*A025225(n). - R. J. Mathar, Oct 18 2013

MAPLE

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

CROSSREFS

Sequence in context: A126429 A098272 A087540 * A136797 A255132 A297332

Adjacent sequences:  A052710 A052711 A052712 * A052714 A052715 A052716

KEYWORD

easy,nonn

AUTHOR

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

STATUS

approved

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Last modified August 23 00:59 EDT 2019. Contains 326211 sequences. (Running on oeis4.)