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 A013708 a(n) = 3^(2n+1). 26
 3, 27, 243, 2187, 19683, 177147, 1594323, 14348907, 129140163, 1162261467, 10460353203, 94143178827, 847288609443, 7625597484987, 68630377364883, 617673396283947, 5559060566555523, 50031545098999707 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS 1/3 + 1/27 + 1/243 + ... = 3/8. - Gary W. Adamson, Aug 29 2008 Number n such that if a=n, b=8n, c=15n, d=36n*sqrt(3n), then a^3 + b^3 + c^3 = d^2; e.g.: a=3, b=24, c=45, d=324, 3^3 + 24^3 + 45^3 = 324^2. - Vincenzo Librandi, Nov 20 2010 LINKS Delbert L. Johnson, Table of n, a(n) for n = 0..1047 Tanya Khovanova, Recursive Sequences R. J. Mathar, Counting Walks on Finite Graphs, Nov 2020, Section 4. Index entries for linear recurrences with constant coefficients, signature (9). FORMULA From Philippe Deléham, Nov 23 2008: (Start) a(n) = 9*a(n-1), n > 0; a(0)=3. G.f.: 3/(1-9x). (End) a(n) = A000244(2n+1). - R. J. Mathar, Jul 10 2015 MATHEMATICA NestList[9#&, 3, 20] (* Harvey P. Dale, Apr 21 2014 *) PROG (PARI) a(n)=3^(2*n+1) \\ Charles R Greathouse IV, Aug 05 2015 (Python) print([3**(2*n+1) for n in range(18)]) # Michael S. Branicky, Mar 27 2021 CROSSREFS Cf. A000244. Sequence in context: A035088 A344724 A268094 * A102518 A361842 A168495 Adjacent sequences: A013705 A013706 A013707 * A013709 A013710 A013711 KEYWORD nonn,easy AUTHOR N. J. A. Sloane STATUS approved

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Last modified December 10 23:37 EST 2023. Contains 367717 sequences. (Running on oeis4.)