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 A002018 From a distribution problem. (Formerly M3652 N1485) 1
 1, 1, 4, 33, 480, 11010, 367560, 16854390, 1016930880, 78124095000, 7446314383200, 862332613342200, 119261328828364800, 19415283189746043600, 3675162134109650184000, 800409618620667941886000, 198730589981586780813696000, 55800304882692417053710704000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES H. Anand, V. C. Dumir and H. Gupta, A combinatorial distribution problem, Duke Math. J., 33 (1996), 757-769. 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 FORMULA a(n) = n*(2*n-1)*b(n) - n*(n-1)^2*b(n-1), b(n) = A000681(n). MATHEMATICA b[n_] := Sum[(2i)!*n!^2/(2^i*i!^2*(n-i)!), {i, 0, n}]/2^n; a[n_] := n*(2n-1)*b[n-1] - n*(n-1)^2*b[n-2]; a[0]=1; Table[a[n], {n, 0, 17}] (* Jean-François Alcover, Aug 08 2012, after formula *) CROSSREFS Sequence in context: A296835 A002190 A101981 * A219504 A258180 A072754 Adjacent sequences:  A002015 A002016 A002017 * A002019 A002020 A002021 KEYWORD nonn,easy,nice AUTHOR EXTENSIONS More terms from David W. Wilson STATUS approved

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Last modified December 6 04:14 EST 2019. Contains 329784 sequences. (Running on oeis4.)