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A221045
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The hyper-Wiener index of the Bethe cactus lattice graph C_n defined pictorially in the Hosoya - Balasubramanian reference.
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1
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10, 792, 22002, 419568, 6592794, 92192136, 1193312130, 14623811808, 172078919466, 1962477443832, 21832497397266, 238041018275280, 2552456907780666, 26988260347784040, 281967905150124450, 2915727266397879744, 29880877053048885834, 303816557606831292120
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OFFSET
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1,1
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REFERENCES
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K. Balasubramanian, Recent developments in tree-pruning methods and polynomials for cactus graphs and trees, J. Math. Chemistry, 4 (1990) 89-102.
H. Hosoya, K. Balasubramanian, Exact dimer statistics and characteristic polynomials of cacti lattices, Theor. Chim. Acta 76 (1989) 315-329.
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LINKS
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FORMULA
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a(n) = (3/2)-3^(n-1)*53+3^(2*n-2)*(64*n^2-148*n)+(97/6)*3^(2*n).
G.f.: 2*x*(5+241*x+495*x^2+27*x^3)/((1-x)*(1-3*x)*(1-9*x)^3). - Bruno Berselli, Dec 30 2012
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MAPLE
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a := proc (n) options operator, arrow: 3/2-53*3^(n-1)+3^(2*n-2)*(64*n^2-148*n)+(97/6)*3^(2*n) end proc: seq(a(n), n = 1 .. 18);
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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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STATUS
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approved
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