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A304839
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a(n) = 61*n - 38 (n>=1).
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1
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23, 84, 145, 206, 267, 328, 389, 450, 511, 572, 633, 694, 755, 816, 877, 938, 999, 1060, 1121, 1182, 1243, 1304, 1365, 1426, 1487, 1548, 1609, 1670, 1731, 1792, 1853, 1914, 1975, 2036, 2097, 2158, 2219, 2280, 2341, 2402, 2463, 2524, 2585, 2646, 2707, 2768, 2829, 2890, 2951, 3012
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OFFSET
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1,1
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COMMENTS
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For n>=2, a(n) is the second Zagreb index of the angular phenylene shown in the Bodroza-Pantic et al. reference (Fig. 1 (b)).
The second Zagreb index of a simple connected graph is the sum of the degree products d(i)d(j) over all edges ij of the graph.
The M-polynomial of the angular phenylene A(n) is M(A(n); x, y) = (n + 4)*x^2*y^2 + 2*n*x^2*y^3 + (5*n - 6)*x^3*y^3.
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LINKS
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FORMULA
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G.f.: x*(23 + 38*x) / (1 - x)^2.
a(n) = 2*a(n-1) - a(n-2) for n>2.
(End)
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MAPLE
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seq(61*n-38, n = 1 .. 50);
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MATHEMATICA
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PROG
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(PARI) Vec(x*(23 + 38*x) / (1 - x)^2 + O(x^40)) \\ Colin Barker, May 24 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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