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A078485
Number of irreducible indecomposable permutations of degree n.
3
0, 1, 1, 1, 7, 15, 31, 63, 127, 255, 511, 1023, 2047, 4095, 8191, 16383, 32767, 65535, 131071, 262143, 524287, 1048575, 2097151, 4194303, 8388607, 16777215, 33554431, 67108863, 134217727, 268435455, 536870911, 1073741823, 2147483647, 4294967295, 8589934591
OFFSET
0,5
LINKS
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.
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
Cf. A134065.
Sequence in context: A317510 A137196 A120094 * A233297 A159695 A014001
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jan 04 2003
STATUS
approved