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 A263231 a(n) = n*(25*n - 39)/2. 5
 0, -7, 11, 54, 122, 215, 333, 476, 644, 837, 1055, 1298, 1566, 1859, 2177, 2520, 2888, 3281, 3699, 4142, 4610, 5103, 5621, 6164, 6732, 7325, 7943, 8586, 9254, 9947, 10665, 11408, 12176, 12969, 13787, 14630, 15498, 16391, 17309, 18252, 19220 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS For n>=3, a(n) = the hyper-Wiener index of the Jahangir graph J_{2,n}. The Jahangir graph J_{2,n} is a connected graph consisting of a cycle graph C(2n) and one additional center vertex that is adjacent to n vertices of C(2n) at distances 2 to each other on C(2n). The Hosoya polynomial of J_{2,n} is 3nx + n(n+3))x^2/2 + n(n-2)x^3 +n(n-3)x^4/2. REFERENCES M. R. Farahani, Hosoya polynomial and Wiener index of Jahangir graphs J_{2,m}, Pacific J. Appl. Math, 7 (3), 2015. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 0..10000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA G.f.: x*(32*x-7)/(1-x)^3. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). MAPLE seq((25*n^2 - 39*n)/2, n=0..40); MATHEMATICA Table[n (25 n - 39)/2, {n, 0, 40}] PROG (PARI) vector(50, n, n--; n*(25*n-39)/2) (PARI) concat(0, Vec(x*(32*x-7)/(1-x)^3 + O(x^100))) \\ Altug Alkan, Oct 18 2015 (Haskell) a263231 n = n * (25 * n - 39) `div` 2 a263231_list = 0 : -7 : 11 : zipWith (+) a263231_list    (map (* 3) \$ tail \$ zipWith (-) (tail a263231_list) a263231_list) -- Reinhard Zumkeller, Nov 04 2015 CROSSREFS Cf. A263226, A263227, A263228, A263229, A263230. Sequence in context: A018508 A038277 A045462 * A077411 A085016 A067690 Adjacent sequences:  A263228 A263229 A263230 * A263232 A263233 A263234 KEYWORD sign,easy AUTHOR Emeric Deutsch, Oct 14 2015 STATUS approved

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Last modified December 15 12:13 EST 2019. Contains 329999 sequences. (Running on oeis4.)