OFFSET
0,5
LINKS
Colin Barker, 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 (3,-2).
FORMULA
a(n) = 2^(n-1) - 1 for n > 3.
G.f.: x - 2*x^3 + x/(1-2*x) - x/(1-x).
(1, 7, 15, 31, 63, ...) = row sums of triangle A134065. - Gary W. Adamson, Oct 06 2007
a(n) = 3*a(n-1) - 2*a(n-2) for n > 2. - Colin Barker, May 27 2016
PROG
(PARI) concat(0, Vec(x*(1-2*x+6*x^3-4*x^4)/((1-x)*(1-2*x)) + O(x^50))) \\ Colin Barker, May 27 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jan 04 2003
STATUS
approved