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%I #30 Sep 08 2022 08:44:28
%S 1,4,16,78,456,3120,24480,216720,2136960,23224320,275788800,
%T 3552595200,49337164800,734788454400,11681891020800,197458829568000,
%U 3535951491072000,66869236482048000,1331693730791424000,27856727993622528000,610658404052336640000
%N a(n) = (n+1)!/2 + (n-1)(n-1)!.
%H Vincenzo Librandi, <a href="/A000780/b000780.txt">Table of n, a(n) for n = 1..200</a>
%H INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=392">Encyclopedia of Combinatorial Structures 392</a>
%H J. R. Stembridge, <a href="http://dx.doi.org/10.1090/S0002-9947-97-01805-9">Some combinatorial aspects of reduced words in finite Coxeter groups</a>, Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332.
%F a(n) = (n-1)!* (n^2+3*n-2)/2. - _Gary Detlefs_, May 22 2010
%p seq((n-1)!* (n^2+3*n-2)/2, n = 1..19); # _Gary Detlefs_, May 22 2010
%t Table[(n + 1)!/2 + (n - 1)*(n - 1)!, {n, 40}] (* _Vladimir Joseph Stephan Orlovsky_, Feb 23 2012 *)
%o (Magma) [Factorial(n+1)/2+(n-1)*Factorial(n-1): n in [1..25]]; // _Vincenzo Librandi_, Jun 07 2013
%K nonn
%O 1,2
%A _N. J. A. Sloane_