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A192513
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Number of Hamiltonian cycles in the 3-ary de Bruijn graph.
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2
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2, 4, 24, 64, 512, 1728, 13312, 32768, 373248, 1310720, 10903552, 35831808, 287965184, 1240465408, 10319560704, 26843545600, 331895275520, 1253826625536, 10690521726976, 34359738368000, 347727917481984, 1307761908383744, 11445236333019136, 30814043149172736
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OFFSET
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1,1
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COMMENTS
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The 3-ary de Bruijn graph is the graph with 3*n nodes {0..3*n-1} and edges from each i to 3*i (mod 3*n), 3*i+1 (mod 3*n), and 3*i+2 (mod 3*n).
Correctness of a(n) = A094678(n)*2^(n-1) for all n>1 follows from S. H. Chan et al. below, together with the BEST theorem. [Dmitrii Pasechnik, Dec 07 2014]
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LINKS
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Table of n, a(n) for n=1..24.
Swee Hong Chan, Henk D. L. Hollmann, Dmitrii V. Pasechnik, Sandpile groups of generalized de Bruijn and Kautz graphs and circulant matrices over finite fields, arXiv:1405.0113 [math.CO], (1-May-2014).
Swee Hong Chan, Henk D. L. Hollmann, Dmitrii V. Pasechnik, Sandpile groups of generalized de Bruijn and Kautz graphs and circulant matrices over finite fields, Journal of Algebra (2015), pp. 268-295.
Wikipedia, BEST Theorem [Dmitrii Pasechnik, Dec 07 2014]
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FORMULA
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a(n) = A094678(n)*2^(n-1) for n > 1. [Joerg Arndt, Dec 07 2014, amended by Georg Fischer, Jun 21 2020]
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MATHEMATICA
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p = 3; numNormalp[n_] := Module[{r, i, pp = 1}, Do[r = MultiplicativeOrder[p, d]; i = EulerPhi[d]/r; pp *= (1 - 1/p^r)^i, {d, Divisors[n]}]; Return[pp]];
a[n_] := Module[{t = 1, q = n, pp}, While[0 == Mod[q, p], q /= p; t += 1]; pp = numNormalp[q]; pp *= p^n/n; Return[pp*2^(n - 1)]];
Array[a, 30] (* Jean-François Alcover, Jul 22 2018, after Joerg Arndt *)
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PROG
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(PARI) a(n)=if(n==1, return(2)); my(r, i, t=3^n/n<<(n-1)); fordiv(n/3^valuation(n, 3), d, r=znorder(Mod(3, d)); i=eulerphi(d)/r; t*=(1-1/3^r)^i); t \\ See comments. Charles R Greathouse IV, Jan 03 2013
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CROSSREFS
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Cf. A003474, A094678.
Cf. A003473, A027362.
Sequence in context: A280075 A068506 A272640 * A192384 A119036 A192382
Adjacent sequences: A192510 A192511 A192512 * A192514 A192515 A192516
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KEYWORD
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nonn
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AUTHOR
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Joerg Arndt, Jul 03 2011
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EXTENSIONS
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More terms from Dmitrii Pasechnik, Dec 07 2014
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STATUS
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approved
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