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A001761 a(n) = (2*n)!/(n+1)!.
(Formerly M3635 N1478)
24

%I M3635 N1478

%S 1,1,4,30,336,5040,95040,2162160,57657600,1764322560,60949324800,

%T 2346549004800,99638080819200,4626053752320000,233153109116928000,

%U 12677700308232960000,739781100339240960000,46113021921146019840000

%N a(n) = (2*n)!/(n+1)!.

%C According to the Beineke and Pippert paper, the number of dissections of a disk is given by D(n)=R(n)/(n-2)!, where R(n)=A001761(n-2) is the number of labeled planar 2-trees having n vertices and rooted at a given exterior edge. [Clarified by _M. F. Hasler_, Feb 22 2012]

%C a(n+1) is the number of labeled incomplete ternary trees on n vertices in which each left and middle child have a larger label than their parent. - _Brian Drake_, Jul 28 2008

%C For n>0: a(n) = A173333(2*n,n+1); cf. A006963, A001813. - _Reinhard Zumkeller_, Feb 19 2010

%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H Vincenzo Librandi, <a href="/A001761/b001761.txt">Table of n, a(n) for n = 0..200</a>

%H L. W. Beineke and R. E. Pippert, Enumerating labeled k-dimensional trees and ball dissections, pp. 12-26 of Proceedings of Second Chapel Hill Conference on Combinatorial Mathematics and Its Applications, University of North Carolina, Chapel Hill, 1970. Reprinted in <a href="http://dx.doi.org/10.1007/BF02330563">Math. Annalen, 191 (1971), 87-98</a>.

%H P. J. Cameron, <a href="http://dx.doi.org/10.1093/qmath/38.2.155">Some treelike objects</a>, Quart. J. Math. Oxford, 38 (1987), 155-183. See p. 166 - _N. J. A. Sloane_, Apr 18 2014

%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=80">Encyclopedia of Combinatorial Structures 80</a>

%H K. A. Penson and J.-M. Sixdeniers, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL4/SIXDENIERS/Catalan.html">Integral Representations of Catalan and Related Numbers</a>, J. Integer Sequences, 4 (2001), #01.2.5.

%H K. A. Penson and A. I. Solomon, <a href="http://arXiv.org/abs/quant-ph/0111151">Coherent states from combinatorial sequences</a>, arXiv:quant-ph/0111151, 2001.

%F a(n) = n!*Catalan(n) =n!* A000108(n). - _N. J. A. Sloane_, Apr 18 2014

%F a(n+2) = sum(A038455(n, m), m=1..n), n >= 1. - _Wolfdieter Lang_

%F E.g.f. for this sequence = o.g.f. for A000108. - _Len Smiley_, Dec 07 2001

%F Integral representation as the moment of a positive function on the positive half-axis: in Maple notation, a(n)=int(x^n*(-1/2+exp(-x/4)/sqrt(Pi*x)+erf(sqrt(x)/2)/2), x=0..infinity), n=0, 1... This representation is unique. - _Karol A. Penson_, Aug 21 2001

%F G.f.: If G_N(x)=1+sum('(2*k)!*(x^k)/(k+1)!', 'k'=1..N), G_N(x)=1+2*x/(G(0)-2*x); G(k)=4*x*(k^2)+6*k*x+k+2*x+2-2*x*(2*k+3)*((k+2)^2)/G(k+1) ; (continued fraction). - _Sergei N. Gladkovskii_, Nov 24 2011

%F a(n) = Sum_{k=0..n} (-1)^(n-k) * (n+1)^(k-1) * Stirling1(n,k). - _Paul D. Hanna_, Nov 09 2012

%F G.f.: Q(0) where Q(k) = 1 + x*(2*k+1)*(4*k+1)/(k+1 - 4*x*(k+1)^2*(4*k+3)/(4*x*(k+1)*(4*k+3) + (2*k+3)/Q(k+1) )); (continued fraction ). - _Sergei N. Gladkovskii_, Apr 05 2013

%F G.f.: G(0)/2, where G(k)= 1 + 1/(1 - x/(x + (k+2)/(2*k+2)/(2*k+1)/G(k+1))); (continued fraction). - _Sergei N. Gladkovskii_, Jun 03 2013

%F Let A(x) = sum(k>=0, a(k)*x^k /(2*k)! ) = ( exp(x)-1)/x, then A(x) = 1/Q(0), where Q(k) = 1 - x/( 1 + (2*k+1)/(1 - x/( 1 + 2*(k+1)/Q(k+1) ))); (continued fraction). - _Sergei N. Gladkovskii_, Nov 24 2013

%F From _Ilya Gutkovskiy_, Jan 21 2017: (Start)

%F a(n) ~ sqrt(2)*4^n*n^(n-1)/exp(n).

%F Sum_{n>=0} 1/a(n) = (7*exp(1/4)*sqrt(Pi)*erf(1/2) + 10)/8 = 2.2865189388213215..., where erf() is the error function. (End)

%p seq(mul((n+k), k=2..n), n=0..17); # _Zerinvary Lajos_, Feb 15 2008

%t Table[(2*n)!/(n+1)!,{n,0,20}] (* _Vincenzo Librandi_, Feb 23 2012 *)

%o (MuPAD) combinat::catalan(n)*n! $ n = 0..17; // _Zerinvary Lajos_, Feb 15 2007

%o (Sage) [binomial(2*n,n)/(1+n)*factorial(n) for n in xrange(0, 18)] # _Zerinvary Lajos_, Dec 03 2009

%o (PARI) A001761(n)=binomial(2*n,n+1)*(n-1)! \\ _M. F. Hasler_, Feb 23 2012

%o (PARI) {Stirling1(n, k)=n!*polcoeff(binomial(x, n), k)}

%o {a(n)=sum(k=0,n,(-1)^(n-k)*(n+1)^(k-1)*Stirling1(n,k))} \\ _Paul D. Hanna_, Nov 09 2012

%Y Cf. A000108, A173333, A006963, A001813.

%Y Main diagonal of A255982, A256061.

%K nonn

%O 0,3

%A _N. J. A. Sloane_

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Last modified October 19 09:48 EDT 2018. Contains 316349 sequences. (Running on oeis4.)