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A246985
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Expansion of (1-8*x+14*x^2)/((1-2*x)*(1-3*x)*(1-6*x)).
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1
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1, 3, 11, 49, 251, 1393, 8051, 47449, 282251, 1686433, 10097891, 60526249, 362976251, 2177317873, 13062296531, 78368963449, 470199366251, 2821153019713, 16926788715971, 101560344351049, 609360902796251, 3656161927895953, 21936961102828211, 131621735227521049, 789730317205170251, 4738381620767930593
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OFFSET
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0,2
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COMMENTS
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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)
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LINKS
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FORMULA
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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
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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Signature corrected and Ibeas formula adapted to the offset by Bruno Berselli, Mar 25 2015
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STATUS
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approved
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