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A304515
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a(n) = 159*2^n - 222 (n>=1).
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4
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96, 414, 1050, 2322, 4866, 9954, 20130, 40482, 81186, 162594, 325410, 651042, 1302306, 2604834, 5209890, 10420002, 20840226, 41680674, 83361570, 166723362, 333446946, 666894114, 1333788450, 2667577122, 5335154466, 10670309154, 21340618530, 42681237282, 85362474786, 170724949794, 341449899810, 682899799842, 1365799599906, 2731599200034, 5463198400290, 10926396800802, 21852793601826, 43705587203874
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OFFSET
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1,1
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COMMENTS
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a(n) is the first Zagreb index of the nanostar dendrimer D[n] from the Ghorbani et al. reference.
The first Zagreb index of a simple connected graph is the sum of the squared degrees of its vertices. Alternatively, it is the sum of the degree sums d(i) + d(j) over all edges ij of the graph.
The M-polynomial of D[n] is M(D[n]; x,y) = 12*(2^n - 1)*x^2*y^2 + 3*(5*2^n - 8)*x^2*y^3 + 3*(2*2^n - 3)*x^3*y^3.
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LINKS
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FORMULA
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G.f.: 6*x*(16 + 21*x) / ((1 - x)*(1 - 2*x)).
a(n) = 3*a(n-1) - 2*a(n-2) for n>2.
(End)
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MAPLE
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seq(159*2^n-222, n = 1 .. 40);
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MATHEMATICA
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Rest@ CoefficientList[Series[6 x (16 + 21 x)/((1 - x) (1 - 2 x)), {x, 0, 38}], x] (* or *)
LinearRecurrence[{3, -2}, {96, 414}, 38] (* or *)
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PROG
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(PARI) Vec(6*x*(16 + 21*x) / ((1 - x)*(1 - 2*x)) + O(x^40)) \\ Colin Barker, May 15 2018
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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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STATUS
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approved
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