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 A305271 a(n) = 680*2^n - 548. 4
 132, 812, 2172, 4892, 10332, 21212, 42972, 86492, 173532, 347612, 695772, 1392092, 2784732, 5570012, 11140572, 22281692, 44563932, 89128412, 178257372, 356515292, 713031132, 1426062812, 2852126172, 5704252892, 11408506332, 22817013212, 45634026972, 91268054492, 182536109532, 365072219612 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) is the  first Zagreb index of the polyphenylene dendrimer G[n], defined pictorially in the Arif et al reference (see Fig. 1, where G is shown). 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 polyphenylene dendrimer G[n] is M(G[n]; x, y) = (56*2^n - 40)*x^2*y^2 + (48*2^n - 40)*x^2*y^3 +(36* 2^n - 36)*x^3*y^3 + 4*x^3 *y^4. LINKS Colin Barker, Table of n, a(n) for n = 0..1000 N. E. Arif, Roslan Hasni and Saeid Alikhani, Fourth order and fourth sum connectivity indices of polyphenylene dendrimers, J. Applied Science, 12 (21), 2012, 2279-2282. E. Deutsch and Sandi Klavzar, M-polynomial and degree-based topological indices, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102. Index entries for linear recurrences with constant coefficients, signature (3,-2). FORMULA From Colin Barker, May 31 2018: (Start) G.f.: 4*(33 + 104*x) / ((1 - x)*(1 - 2*x)). a(n) = 3*a(n-1) - 2*a(n-2) for n>1. (End) MAPLE seq(680*2^n-548, n = 0..40); PROG (PARI) Vec(4*(33 + 104*x) / ((1 - x)*(1 - 2*x)) + O(x^40)) \\ Colin Barker, May 31 2018 CROSSREFS Cf. A305269, A305270, A305272. Sequence in context: A115132 A158543 A156958 * A090199 A239598 A033278 Adjacent sequences:  A305268 A305269 A305270 * A305272 A305273 A305274 KEYWORD nonn,easy AUTHOR Emeric Deutsch, May 30 2018 STATUS approved

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Last modified September 17 04:58 EDT 2019. Contains 327119 sequences. (Running on oeis4.)