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
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