A052737 a(n) = ((2*n)!/n!)*2^(2*n+1).

0, 2, 16, 384, 15360, 860160, 61931520, 5449973760, 566797271040, 68015672524800, 9250131463372800, 1406019982432665600, 236211357048687820800, 43462889696958559027200, 8692577939391711805440000, 1877596834908609749975040000, 435602465698797461994209280000

Offset

0,2

Comments

A simple context-free grammar in a labeled universe.

Links

Table of n, a(n) for n=0..16.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 693.

Formula

E.g.f.: 1/4 - (1/4)*sqrt(1-16*x).

D-finite Recurrence: {a(1)=2, (8-16*n)*a(n) + a(n+1)=0}.

a(n) = (1/8)*16^(n+1)*Gamma(n+1/2)/Pi^(1/2).

a(n) = n! * A052707(n). - R. J. Mathar, Aug 21 2014

From Amiram Eldar, Mar 22 2022: (Start)

Sum_{n>=1} 1/a(n) = sqrt(Pi)*exp(1/16)*erf(1/4)/8, where erf is the error function.

Sum_{n>=1} (-1)^(n+1)/a(n) = sqrt(Pi)*exp(-1/16)*erfi(1/4)/8, where erfi is the imaginary error function. (End)

Maple

spec := [S, {B=Union(Z, C), S=Union(B, Z, C), C=Prod(S, S)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
[seq((2*n)!/n!*2^(2*n+1), n=0..12)]; # Zerinvary Lajos, Sep 28 2006

Mathematica

With[{nn=20}, CoefficientList[Series[1/4-Sqrt[1-16x]/4, {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Aug 12 2015 *)

Crossrefs

Cf. A052707.

Sequence in context: A325287 A140308 A280723 * A002474 A172149 A340563

Adjacent sequences: A052734 A052735 A052736 * A052738 A052739 A052740

Keyword

easy,nonn

Author

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

Extensions

Better definition from Zerinvary Lajos, Sep 28 2006

More terms from Harvey P. Dale, Aug 12 2015

Status

approved