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 A048617 a(n) = 2*(n!)^2. 5
 2, 2, 8, 72, 1152, 28800, 1036800, 50803200, 3251404800, 263363788800, 26336378880000, 3186701844480000, 458885065605120000, 77551576087265280000, 15200108913103994880000, 3420024505448398848000000, 875526273394790105088000000, 253027093011094340370432000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) = automorphism group order for the complete bipartite graph K_{n,n}. - Avi Peretz (njk(AT)netvision.net.il), Feb 21 2001 For n > 1, also the order of automorphism group for the n X n rook graph. - Eric W. Weisstein, Jun 20 2017 Also the number of (directed) Hamiltonian paths in K_{n,n}. - Eric W. Weisstein, Jul 15 2011 For n>=1, a(n) is the number of ways to arrange n men and n women in a line so that no two people of the same gender are adjacent. - Geoffrey Critzer, Aug 24 2013 Also the number of (directed) Hamiltonian paths in the (n+1)-barbell graph. - Eric W. Weisstein, Dec 16 2013 LINKS Eric Weisstein's World of Mathematics, Graph Automorphism Eric Weisstein's World of Mathematics, Barbell Graph Eric Weisstein's World of Mathematics, Complete Bipartite Graph Eric Weisstein's World of Mathematics, Hamiltonian Path Eric Weisstein's World of Mathematics, Rook Graph FORMULA a(n) = 2*A001044(n) MAPLE seq(mul(n!*k!, k=1..2), n=0..17); # Zerinvary Lajos, Jul 01 2007 MATHEMATICA 2(Range[0, 20]!)^2 (* Harvey P. Dale, Jun 21 2011 *) Table[2 (n!)^2, {n, 0, 20}] (* Vincenzo Librandi, Feb 22 2016 *) PROG (MAGMA) [2*Factorial(n)^2: n in [0..30]]; // Vincenzo Librandi, Feb 22 2016 CROSSREFS Equals 2 * A001044. Sequence in context: A003181 A009616 A005615 * A000615 A297010 A012413 Adjacent sequences:  A048614 A048615 A048616 * A048618 A048619 A048620 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 20 06:56 EDT 2021. Contains 345157 sequences. (Running on oeis4.)