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A304828
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a(n) = 344*7^n/21 - 128/3 (n>=1).
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2
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72, 760, 5576, 39288, 275272, 1927160, 13490376, 94432888, 661030472, 4627213560, 32390495176, 226733466488, 1587134265672, 11109939859960, 77769579019976, 544387053140088, 3810709371980872, 26674965603866360, 186724759227064776, 1307073314589453688, 9149513202126176072
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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 crystal structure cubic carbon CCC(n), defined in the Baig et al. and in the Gao et al. references.
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.
For n>=2 the M-polynomial of the crystal structure cubic carbon CCC(n) is M(CCC(n); x,y) = 72*7^(n-2)*x^3*y^3 + 24*7^(n-2)*x^3*y^4 + (76*7^(n-2) - 16)*x^4*y^4/3.
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LINKS
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FORMULA
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G.f.: 8*x*(9 + 23*x) / ((1 - x)*(1 - 7*x)).
a(n) = 8*a(n-1) - 7*a(n-2) for n>2. (End)
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MAPLE
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seq((344*7^(n-1)-128)*(1/3), n = 1 .. 25);
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MATHEMATICA
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LinearRecurrence[{8, -7}, {72, 760}, 30] (* Harvey P. Dale, Aug 24 2019 *)
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PROG
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(PARI) Vec(8*x*(9 + 23*x) / ((1 - x)*(1 - 7*x)) + O(x^30)) \\ Colin Barker, May 21 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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