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 A048921 9-gonal heptagonal numbers (A000566). 3
 1, 26884, 542041975, 10928650279834, 220343446399977901, 4442564555387704166896, 89570986345383445012986019, 1805930222253056462964119954950, 36411165051495138060899141518722649, 734121907962314751330792028336366100956 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS As n increases, this sequence is approximately geometric with common ratio r = lim(n->Infinity,a(n)/a(n-1)) = (6+sqrt(35))^4 = 10081+1704*sqrt(35). - Ant King, Dec 31 2011 LINKS Colin Barker, Table of n, a(n) for n = 1..233 Eric Weisstein's World of Mathematics, Nonagonal Heptagonal Number. Index entries for linear recurrences with constant coefficients, signature (20163,-20163,1). FORMULA From Ant King, Dec 31 2011: (Start) a(n) = 20163*a(n-1)-20163*a(n-2)+a(n-3). a(n) = 20162*a(n-1)-a(n-2)+6768. a(n) = 1/560*((39+4*sqrt(35))*(6+sqrt(35))^(4*n-3)+(39-4*sqrt(35))*(6-sqrt(35))^(4*n-3)-188). a(n) = floor(1/560*(39+4*sqrt(35))*(6+sqrt(35))^(4*n-3)). G.f.: x(1+6721*x+46*x^2) / ((1-x)(1-20162*x+x^2)). (End) MATHEMATICA LinearRecurrence[{20163, -20163, 1}, {1, 26884, 542041975}, 9]; (* Ant King, Dec 31 2011 *) PROG (PARI) Vec(x*(1+6721*x+46*x^2)/((1-x)*(1-20162*x+x^2)) + O(x^20)) \\ Colin Barker, Jun 22 2015 CROSSREFS Cf. A048919, A048920. Sequence in context: A235814 A199547 A051025 * A269115 A249496 A227348 Adjacent sequences:  A048918 A048919 A048920 * A048922 A048923 A048924 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified October 17 21:32 EDT 2019. Contains 328133 sequences. (Running on oeis4.)