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A074528 a(n) = 2^n + 3^n + 6^n. 5
3, 11, 49, 251, 1393, 8051, 47449, 282251, 1686433, 10097891, 60526249, 362976251, 2177317873, 13062296531, 78368963449, 470199366251, 2821153019713, 16926788715971, 101560344351049, 609360902796251 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

From Álvar Ibeas, Mar 24 2015: (Start)

Number of isomorphism classes of 3-fold coverings of a connected graph with circuit rank n+1 [Kwak and Lee].

Number of orbits of the conjugacy action of Sym(3) on Sym(3)^(n+1) [Kwak and Lee, 2001].

(End)

REFERENCES

J. H. Kwak and J. Lee, Enumeration of graph coverings, surface branched coverings and related group theory, in Combinatorial and Computational Mathematics (Pohang, 2000), ed. S. Hong et al., World Scientific, Singapore 2001, pp. 97-161. [Added by N. J. A. Sloane, Nov 12 2009]

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

M. W. Hero and J. F. Willenbring, Stable Hilbert series as related to the measurement of quantum entanglement, Discrete Math., 309 (2010), 6508-6514.

J. H. Kwak and J. Lee, Isomorphism classes of graph bundles. Can. J. Math., 42(4), 1990, pp. 747-761.

Index entries for linear recurrences with constant coefficients, signature (11,-36,36).

FORMULA

G.f.: 1/(1-2*x)+1/(1-3*x)+1/(1-6*x). E.g.f.: exp(2*x)+exp(3*x)+exp(6*x). - Mohammad K. Azarian, Dec 26 2008

MATHEMATICA

Table[2^n + 3^n + 6^n, {n, 0, 20}]

LinearRecurrence[{11, -36, 36}, {3, 11, 49}, 30] (* Harvey P. Dale, May 02 2016 *)

PROG

(MAGMA) [2^n + 3^n + 6^n: n in [0..25]]; // Vincenzo Librandi, Jun 11 2011

(PARI) a(n)=2^n+3^n+6^n \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Cf. A001550, A001576, A034513, A001579, A074501-A074580.

A246985 is essentially identical.

Third row of A160449, shifted.

Sequence in context: A172440 A254536 A268414 * A246985 A004211 A180869

Adjacent sequences:  A074525 A074526 A074527 * A074529 A074530 A074531

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Aug 23 2002

STATUS

approved

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Last modified October 19 22:00 EDT 2018. Contains 316378 sequences. (Running on oeis4.)