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 A078484 G.f.: -x*(1-2*x+2*x^2)/(2*x^3-4*x^2+4*x-1). 3
 0, 1, 2, 6, 18, 52, 148, 420, 1192, 3384, 9608, 27280, 77456, 219920, 624416, 1772896, 5033760, 14292288, 40579904, 115217984, 327136896, 928835456, 2637230208, 7487852800, 21260161280, 60363694336, 171389837824, 486624896512, 1381667623424, 3922950583296 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS Enumerates pop-stacks. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 M. D. Atkinson and T. Stitt, Restricted permutations and the wreath product, Preprint, 2002. M. D. Atkinson and T. Stitt, Restricted permutations and the wreath product, Discrete Math., 259 (2002), 19-36. Index entries for linear recurrences with constant coefficients, signature (4, -4, 2). FORMULA a(0)=0, a(1)=1, a(2)=2, a(3)=6, a(n) = 4*a(n-1)-4*a(n-2)+2*a(n-3). - Harvey P. Dale, Jul 21 2012 MATHEMATICA CoefficientList[Series[-x(1-2x+2x^2)/(2x^3-4x^2+4x-1), {x, 0, 30}], x] (* or *) Join[{0}, LinearRecurrence[{4, -4, 2}, {1, 2, 6}, 30]] (* Harvey P. Dale, Jul 21 2012 *) CROSSREFS Sequence in context: A128104 A318570 A027059 * A156989 A077935 A077835 Adjacent sequences:  A078481 A078482 A078483 * A078485 A078486 A078487 KEYWORD nonn AUTHOR N. J. A. Sloane, Jan 04 2003 EXTENSIONS Replaced definition with g.f. given by Atkinson and Stitt (2002). - N. J. A. Sloane, May 24 2016 STATUS approved

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Last modified April 20 06:19 EDT 2019. Contains 322294 sequences. (Running on oeis4.)