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 A304166 a(n) = 972*n^2 - 1224*n + 414 with n > 0. 2
 162, 1854, 5490, 11070, 18594, 28062, 39474, 52830, 68130, 85374, 104562, 125694, 148770, 173790, 200754, 229662, 260514, 293310, 328050, 364734, 403362, 443934, 486450, 530910, 577314, 625662, 675954, 728190, 782370, 838494, 896562, 956574, 1018530, 1082430, 1148274, 1216062, 1285794, 1357470, 1431090, 1506654 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) provides the second Zagreb index of the HcDN1(n) network (see Fig. 3 in the Hayat et al. paper). 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 HcDN1(n) is M(HcDN1(n); x,y) = 6x^3*y^3 + 12(n-1)x^3*y^5 + 6nx^3*y^6 + 18(n-1)x^5*y^6 + (27n^2 - 57n + 30)x^6*y^6. - Emeric Deutsch, May 11 2018 LINKS Colin Barker, Table of n, a(n) for n = 1..1000 E. Deutsch and Sandi Klavzar, M-polynomial and degree-based topological indices, Iranian J. Math. Chemistry, 6, No. 2, 2015, 93-102. S. Hayat, M. A. Malik, and M. Imran, Computing topological indices of honeycomb derived networks, Romanian J. of Information Science and Technology, 18, No. 2, 2015, 144-165. Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA From Colin Barker, May 10 2018: (Start) G.f.: 18*x*(9 + 76*x + 23*x^2) / (1 - x)^3. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>3. (End) MAPLE seq(972*n^2-1224*n+414, n = 1 .. 40); PROG (PARI) a(n) = 972*n^2-1224*n+414; \\ Altug Alkan, May 09 2018 (PARI) Vec(18*x*(9 + 76*x + 23*x^2) / (1 - x)^3 + O(x^60)) \\ Colin Barker, May 10 2018 CROSSREFS Cf. A304163, A304164, A304165. Sequence in context: A319915 A302731 A206145 * A213288 A302532 A288489 Adjacent sequences:  A304163 A304164 A304165 * A304167 A304168 A304169 KEYWORD nonn,easy AUTHOR Emeric Deutsch, May 09 2018 STATUS approved

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Last modified April 24 20:29 EDT 2019. Contains 322446 sequences. (Running on oeis4.)