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 A305272 a(n) = 836*2^n - 676. 4
 160, 996, 2668, 6012, 12700, 26076, 52828, 106332, 213340, 427356, 855388, 1711452, 3423580, 6847836, 13696348, 27393372, 54787420, 109575516, 219151708, 438304092, 876608860, 1753218396, 3506437468, 7012875612, 14025751900, 28051504476, 56103009628, 112206019932, 224412040540, 448824081756 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) is the second Zagreb index of the polyphenylene dendrimer G[n], defined pictorially in the Arif et al. reference (see Fig. 1, where G[2] is shown). 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 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*(40 + 129*x) / ((1 - x)*(1 - 2*x)). a(n) = 3*a(n-1) - 2*a(n-2) for n>1. (End) MAPLE seq(836*2^n-676, n = 0..40); MATHEMATICA 836*2^Range[0, 40]-676 (* or *) LinearRecurrence[{3, -2}, {160, 996}, 40] (* Harvey P. Dale, Jun 19 2021 *) PROG (PARI) Vec(4*(40 + 129*x) / ((1 - x)*(1 - 2*x)) + O(x^40)) \\ Colin Barker, May 31 2018 CROSSREFS Cf. A305269, A305270, A305271. Sequence in context: A234651 A234898 A234891 * A234450 A234444 A166778 Adjacent sequences: A305269 A305270 A305271 * A305273 A305274 A305275 KEYWORD nonn,easy AUTHOR Emeric Deutsch, May 30 2018 STATUS approved

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Last modified June 12 19:52 EDT 2024. Contains 373360 sequences. (Running on oeis4.)