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 A047053 a(n) = 4^n * n!. 40
 1, 4, 32, 384, 6144, 122880, 2949120, 82575360, 2642411520, 95126814720, 3805072588800, 167423193907200, 8036313307545600, 417888291992371200, 23401744351572787200, 1404104661094367232000, 89862698310039502848000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Original name was "Quadruple factorial numbers". For n >= 1, a(n) is the order of the wreath product of the symmetric group S_n and the Abelian group (C_4)^n. - Ahmed Fares (ahmedfares(AT)my-deja.com), May 07 2001 Number of n X n monomial matrices with entries 0, +/-1, +/-i. a(n) is the product of the positive integers <= 4*n that are multiples of 4. - Peter Luschny, Jun 23 2011 Also, a(n) is the number of signed permutations of length 2*n that are equal to their reverse-complements. (See the Hardt and Troyka reference.) - Justin M. Troyka, Aug 13 2011. Pi^n/a(n) is the volume of a 2*n-dimensional ball with radius 1/2. - Peter Luschny, Jul 24 2012 Equals the first right hand column of A167557, and also equals the first right hand column of A167569. - Johannes W. Meijer, Nov 12 2009 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..100 R. B. Brent, Generalizing Tuenter's Binomial Sums, J. Int. Seq. 18 (2015), # 15.3.2. R. Coquereaux, J.-B. Zuber, Maps, immersions and permutations, arXiv preprint arXiv:1507.03163 [math.CO], 2015-2016. Also J. Knot Theory Ramifications 25, 1650047 (2016), DOI. Sylvie Corteel and Lauren Williams, Tableaux Combinatorics for the Asymmetric Exclusion Process II, arXiv:0810.2916 [math.CO], 2008-2009. [From Jonathan Vos Post, Oct 17 2008] A. Hardt and J. M. Troyka, Restricted symmetric signed permutations, Pure Mathematics and Applications, Vol. 23 (No. 3, 2012), pp. 179-217. A. Hardt and J. M. Troyka, Slides (associated with the Hardt and Troyka reference above). INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 492. Alexsandar Petojevic, The Function vM_m(s; a; z) and Some Well-Known Sequences, Journal of Integer Sequences, 5 (2002), Article 02.1.7. M. D. Schmidt, Generalized j-Factorial Functions, Polynomials, and Applications, J. Int. Seq. 13 (2010), Article 10.6.7, p. 39. Michael Z. Spivey and Laura L. Steil, The k-Binomial Transforms and the Hankel Transform, Journal of Integer Sequences, 9 (2006), Article 06.1.1. FORMULA a(n) = 4^n * n!. E.g.f.: 1/(1 - 4*x). Integral representation as the n-th moment of a positive function on a positive half-axis: in Maple notation a(n) = int(x^n*exp(-4*x)/4, x=0..infinity), n = 0, 1, ... This representation is unique. - Karol A. Penson, Jan 28 2002 Sum_{k>=0} (-1)^k/(2*k + 1)^n = (-1)^n * n * (PolyGamma[n-1, 1/4] - PolyGamma[n-1, 3/4]) / a(n) for n > 0. - Joseph Biberstine (jrbibers(AT)indiana.edu), Jul 27 2006 a(n) = Sum_{k=0..n} C(n,k)*(2k)!*(2(n-k))!/(k!(n-k)!) = Sum_{k=0..n} C(n,k)*A001813(k)*A001813(n-k). - Paul Barry, May 04 2007 E.g.f.: With interpolated zeros, 1 + sqrt(pi)*x*exp(x^2)*erf(x). - Paul Barry, Apr 10 2010 From Gary W. Adamson, Jul 19 2011: (Start) a(n) = sum of top row terms of M^n, M = an infinite square production matrix as follows:   2, 2, 0, 0, 0, 0, ...   4, 4, 4, 0, 0, 0, ...   6, 6, 6, 6, 0, 0, ...   8, 8, 8, 8, 8, 0, ...   ... (End) G.f.: 1/(1 - 4*x/(1 - 4*x/(1 - 8*x/(1 - 8*x/(1 - 12*x/(1 - 12*x/(1 - 16*x/1 - ... (continued fraction). - Philippe Deléham, Jan 08 2012 G.f.: 2/G(0), where G(k) = 1 + 1/(1 - 8*x*(k + 1)/(8*x*(k + 1) - 1 + 8*x*(k + 1)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 30 2013 G.f.: 1/Q(0), where Q(k) = 1 - 4*x*(2*k + 1) - 16*x^2*(k + 1)^2/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Sep 28 2013 a(n) = A000142(n) * A000302(n). - Michel Marcus, Nov 28 2013 a(n) = A087299(2*n). - Michael Somos, Jan 03 2015 D-finite with recurrence: a(n) - 4*n*a(n-1) = 0. - R. J. Mathar, Jan 27 2020 From Amiram Eldar, Jun 25 2020: (Start) Sum_{n>=0) 1/a(n) = e^(1/4) (A092042). Sum_{n>=0) (-1)^n/a(n) = e^(-1/4) (A092616). (End) EXAMPLE G.f. = 1 + 4*x + 32*x^2 + 384*x^3 + 6144*x^4 + 122880*x^5 + 2949120*x^6 + ... MAPLE A047053:= n -> mul(k, k = select(k-> k mod 4 = 0, [\$1..4*n])): seq(A047053(n), n = 0.. 16); # Peter Luschny, Jun 23 2011 MATHEMATICA a[n_]:= With[{m=2n}, If[ m<0, 0, m!*SeriesCoefficient[1 +Sqrt[Pi]*x*Exp[x^2]*Erf[x], {x, 0, m}]]]; (* Michael Somos, Jan 03 2015 *) PROG (PARI)  a(n)=4^n*n!; (MAGMA) [4^n*Factorial(n): n in [0..20]]; // Vincenzo Librandi, Jul 20 2011 CROSSREFS Cf. A000142, A000165, A007696, A008545, A032031, A087299, A092042, A092616. a(n)= A051142(n+1, 0) (first column of triangle). Sequence in context: A051489 A295257 A303049 * A201594 A222412 A007763 Adjacent sequences:  A047050 A047051 A047052 * A047054 A047055 A047056 KEYWORD nonn,easy AUTHOR Joe Keane (jgk(AT)jgk.org) EXTENSIONS Edited by Karol A. Penson, Jan 22 2002 STATUS approved

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Last modified October 20 13:48 EDT 2020. Contains 337904 sequences. (Running on oeis4.)