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 A304508 a(n) = 5*(3*n+1)*(9*n+8)/2 (n>=0). 2
 20, 170, 455, 875, 1430, 2120, 2945, 3905, 5000, 6230, 7595, 9095, 10730, 12500, 14405, 16445, 18620, 20930, 23375, 25955, 28670, 31520, 34505, 37625, 40880, 44270, 47795, 51455, 55250, 59180, 63245, 67445, 71780, 76250, 80855, 85595, 90470, 95480, 100625, 105905, 111320 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The second Zagreb index of the single-defect  5-gonal nanocone CNC(5,n) (see definition in the Doslic et al. reference, p. 27). 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 CNC(5,n) is M(CNC(5,n); x,y) = 5*x^2*y^2 + 10*n*x^2*y^3 + 5*n*(3*n+1)*x^3*y^3/2. More generally, the M-polynomial of CNC(k,n) is M(CNC(k,n); x,y) = k*x^2*y^2 + 2*k*n*x^2*y^3 + k*n*(3*n + 1)*x^3*y^3/2. LINKS Colin Barker, Table of n, a(n) for n = 0..1000 E. Deutsch and Sandi Klavzar, M-polynomial and degree-based topological indices, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102. T. Doslic and M. Saheli, Augmented eccentric connectivity index of single-defect nanocones, J. of Mathematical Nanoscience, 1, No. 1, 2011, 25-31. A. Khaksar, M. Ghorbani, and H. R. Maimani, On atom bond connectivity and GA indices of nanocones, Optoelectronics and Advanced Materials - Rapid Communications, 4, No. 11, 2010, 1868-1870. Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA From Colin Barker, May 14 2018: (Start) G.f.: 5*(4 + 22*x + x^2) / (1 - x)^3. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>2. (End) MAPLE seq((1/2)*(5*(3*n+1))*(9*n+8), n = 0 .. 40); MATHEMATICA Array[5 (3 # + 1) (9 # + 8)/2 &, 41, 0] (* or *) LinearRecurrence[{3, -3, 1}, {20, 170, 455}, 41] (* or *) CoefficientList[Series[5 (4 + 22 x + x^2)/(1 - x)^3, {x, 0, 40}], x] (* Michael De Vlieger, May 14 2018 *) PROG (PARI) a(n) = 5*(3*n+1)*(9*n+8)/2; \\ Altug Alkan, May 14 2018 (PARI) Vec(5*(4 + 22*x + x^2) / (1 - x)^3 + O(x^40)) \\ Colin Barker, May 14 2018 CROSSREFS Cf. A304507. Sequence in context: A186259 A292281 A056932 * A010826 A022712 A056128 Adjacent sequences:  A304505 A304506 A304507 * A304509 A304510 A304511 KEYWORD nonn,easy AUTHOR Emeric Deutsch, May 14 2018 STATUS approved

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Last modified March 21 04:59 EDT 2019. Contains 321364 sequences. (Running on oeis4.)