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 A304505 a(n) = 4*(n+1)*(9*n+4). 2
 16, 104, 264, 496, 800, 1176, 1624, 2144, 2736, 3400, 4136, 4944, 5824, 6776, 7800, 8896, 10064, 11304, 12616, 14000, 15456, 16984, 18584, 20256, 22000, 23816, 25704, 27664, 29696, 31800, 33976, 36224, 38544, 40936, 43400, 45936, 48544, 51224, 53976, 56800, 59696 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) is the first Zagreb index of the single-defect 4-gonal nanocone CNC(4,n) (see definition in the Doslic et al. reference, p. 27). 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 CNC(4,n) is M(CNC(4,n); x,y) = 4*x^2*y^2 + 8*n*x^2*y^3 + 2*n*(3*n+1)*x^3*y^3. 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. 9*a(n) + 25 is a square. - Bruno Berselli, May 14 2018 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.: 8*(2 + 7*x) / (1 - x)^3. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>2. (End) MAPLE seq((4*(n+1))*(9*n+4), n = 0 .. 40); PROG (PARI) a(n) = 4*(n+1)*(9*n+4); \\ Altug Alkan, May 14 2018 (GAP) List([0..50], n->4*(n+1)*(9*n+4)); # Muniru A Asiru, May 14 2018 (PARI) Vec(8*(2 + 7*x) / (1 - x)^3 + O(x^40)) \\ Colin Barker, May 14 2018 CROSSREFS Cf. A304506. Sequence in context: A240257 A199773 A245872 * A210687 A000739 A186852 Adjacent sequences:  A304502 A304503 A304504 * A304506 A304507 A304508 KEYWORD nonn,easy AUTHOR Emeric Deutsch, May 14 2018 STATUS approved

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Last modified July 8 01:25 EDT 2020. Contains 335502 sequences. (Running on oeis4.)