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 A000780 a(n) = (n+1)!/2+(n-1)(n-1)!. 1
 1, 4, 16, 78, 456, 3120, 24480, 216720, 2136960, 23224320, 275788800, 3552595200, 49337164800, 734788454400, 11681891020800, 197458829568000, 3535951491072000, 66869236482048000, 1331693730791424000, 27856727993622528000, 610658404052336640000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..200 INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 392 J. R. Stembridge, Some combinatorial aspects of reduced words in finite Coxeter groups, Trans. Amer. Math. Soc. 349 (1997), no. 4, 1285-1332. FORMULA a(n) = (n-1)!* (n^2+3*n-2)/2. - Gary Detlefs, May 22 2010 MAPLE seq((n-1)!* (n^2+3*n-2)/2, n = 1..19); # Gary Detlefs, May 22 2010 MATHEMATICA Table[(n + 1)!/2 + (n - 1)*(n - 1)!, {n, 40}] (* Vladimir Joseph Stephan Orlovsky, Feb 23 2012 *) PROG (MAGMA) [Factorial(n+1)/2+(n-1)*Factorial(n-1): n in [1..25]]; // Vincenzo Librandi, Jun 07 2013 CROSSREFS Sequence in context: A204208 A138294 A014514 * A002713 A221763 A009318 Adjacent sequences:  A000777 A000778 A000779 * A000781 A000782 A000783 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 4 01:32 EDT 2020. Contains 334809 sequences. (Running on oeis4.)