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 A002691 a(n) = (n+2) * (2n+1) * (2n-1)! / (n-1)!. (Formerly M4661 N1996) 5
 1, 9, 120, 2100, 45360, 1164240, 34594560, 1167566400, 44108064000, 1843717075200, 84475764172800, 4209708914611200, 226676633863680000, 13114862387827200000, 811372819726909440000, 53449184499510159360000, 3735154775612827607040000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Coefficients of orthogonal polynomials. REFERENCES N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Alois P. Heinz, Table of n, a(n) for n = 0..150 H. E. Salzer, Orthogonal polynomials arising in the evaluation of inverse Laplace transforms, Math. Comp. 9 (1955), 164-177. H. E. Salzer, Orthogonal polynomials arising in the evaluation of inverse Laplace transforms, Math. Comp. 9 (1955), 164-177. [Annotated scanned copy] FORMULA E.g.f.: (1-x)/(1-4*x)^(5/2). Conjecture: a(n) +4*(-n-1)*a(n-1) +4*(-2*n+1)*a(n-2)=0. - R. J. Mathar, Jun 07 2013 MAPLE with(combstruct): a:=n-> add((count(Permutation(n*2+1), size=n+1)), j=0..n+1)/2: seq(a(n), n=0..16); # Zerinvary Lajos, May 03 2007 MATHEMATICA Join[{1}, Table[(n+2)(2n+1)(2n-1)!/(n-1)!, {n, 15}]] (* Harvey P. Dale, Jun 09 2011 *) PROG (PARI) a(n)=(n+2)*(2*n+1)*(2*n-1)!/(n-1)! CROSSREFS Cf. A002690. Sequence in context: A167593 A214698 A024487 * A234320 A157930 A259836 Adjacent sequences:  A002688 A002689 A002690 * A002692 A002693 A002694 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS Edited by Ralf Stephan, Mar 21 2004 STATUS approved

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Last modified May 30 17:45 EDT 2020. Contains 334728 sequences. (Running on oeis4.)