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A305159
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a(n) = 102*2^n - 78.
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3
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24, 126, 330, 738, 1554, 3186, 6450, 12978, 26034, 52146, 104370, 208818, 417714, 835506, 1671090, 3342258, 6684594, 13369266, 26738610, 53477298, 106954674, 213909426, 427818930, 855637938, 1711275954, 3422551986, 6845104050, 13690208178, 27380416434, 54760832946, 109521665970, 219043332018
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OFFSET
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0,1
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COMMENTS
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a(n) is the first Zagreb index of the all-aromatic dendrimer G[n], shown pictorially as DNS1[n] in the Shabani et al. reference (Fig. 1).
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 the dendrimer G[n] is M(G[n]; x, y) = 6*2^n*x^2*y^2 + 12*(2^n - 1)*x^2*y^3 +3* (2^n - 1)*x^3*y^3.
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LINKS
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FORMULA
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G.f.: 6*(4 + 9*x) / ((1 - x)*(1 - 2*x)).
a(n) = 3*a(n-1) - 2*a(n-2) for n>1.
(End)
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MAPLE
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seq(102*2^n-78, n = 0..40);
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PROG
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(PARI) Vec(6*(4 + 9*x) / ((1 - x)*(1 - 2*x)) + O(x^40)) \\ Colin Barker, May 30 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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