OFFSET
0,2
COMMENTS
From Álvar Ibeas, Mar 25 2015: (Start)
Number of isomorphism classes of 3-fold coverings of a connected graph with circuit rank n [Kwak and Lee].
Number of orbits of the conjugacy action of Sym(3) on Sym(3)^n [Kwak and Lee].
(End)
LINKS
J. H. Kwak and J. Lee, Isomorphism classes of graph bundles. Can. J. Math., 42(4), 1990, pp. 747-761.
A. Prasad, Equivalence classes of nodes in trees and rational generating functions, arXiv:1407.5284 [math.CO], 2014.
Index entries for linear recurrences with constant coefficients, signature (11,-36,36).
FORMULA
G.f.: (1-8*x+14*x^2)/((1-2*x)*(1-3*x)*(1-6*x)).
a(n) = 11*a(n-1) - 36*a(n-2) + 36*a(n-3) for n>2. [Bruno Berselli, Mar 25 2015]
a(n) = 2^(n-1) + 3^(n-1) + 6^(n-1). - Álvar Ibeas, Mar 25 2015
MATHEMATICA
Table[2^(n - 1) + 3^(n - 1) + 6^(n - 1), {n, 0, 30}] (* Bruno Berselli, Mar 25 2015 *)
LinearRecurrence[{11, -36, 36}, {1, 3, 11}, 30] (* Harvey P. Dale, Jan 17 2019 *)
PROG
(Magma) [n le 3 select 2*Factorial(n)-1 else 11*Self(n-1)-36*Self(n-2)+36*Self(n-3): n in [1..30]];
(PARI) Vec((1-8*x+14*x^2)/((1-2*x)*(1-3*x)*(1-6*x)) + O(x^30)) \\ Michel Marcus, Jan 14 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Sep 15 2014
EXTENSIONS
Signature corrected and Ibeas formula adapted to the offset by Bruno Berselli, Mar 25 2015
STATUS
approved