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 A097321 a(n) = (3*n-1) * 3*n * (3*n+1). 6
 24, 210, 720, 1716, 3360, 5814, 9240, 13800, 19656, 26970, 35904, 46620, 59280, 74046, 91080, 110544, 132600, 157410, 185136, 215940, 249984, 287430, 328440, 373176, 421800, 474474, 531360, 592620, 658416, 728910, 804264, 884640 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..10000 S. Ramanujan, Notebook entry Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1). FORMULA G.f.: 6x * (4x^2 + 19x + 4) / (1-x)^4. Sum_{n>=1} 1/a(n) = (log(3) - 1)/2. - Amiram Eldar, Jul 04 2020 MATHEMATICA Table[27n^3-3n, {n, 40}]  (* Harvey P. Dale, Mar 30 2011 *) PROG (MAGMA) [27*n^3-3*n: n in [1..40]]; // Vincenzo Librandi, Sep 07 2011 CROSSREFS Cf. A069072, A069140, A002391, A016767. Sequence in context: A283540 A047659 A108671 * A105946 A050222 A169635 Adjacent sequences:  A097318 A097319 A097320 * A097322 A097323 A097324 KEYWORD nonn,easy AUTHOR Ralf Stephan, Aug 07 2004 STATUS approved

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Last modified November 30 18:31 EST 2021. Contains 349424 sequences. (Running on oeis4.)