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 A140681 a(n) = 3*n*(n+6). 13
 0, 21, 48, 81, 120, 165, 216, 273, 336, 405, 480, 561, 648, 741, 840, 945, 1056, 1173, 1296, 1425, 1560, 1701, 1848, 2001, 2160, 2325, 2496, 2673, 2856, 3045, 3240, 3441, 3648, 3861, 4080, 4305, 4536, 4773, 5016, 5265, 5520, 5781 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..5000 Index entries for linear recurrences with constant coefficients, signature (3,-3,1). FORMULA a(n) = A028560(n)*3 = 3*n^2 + 18*n = n*(3*n+18). a(n) = 6*n + a(n-1) + 15 with n>0, a(0)=0. - Vincenzo Librandi, Aug 03 2010 from G. C. Greubel, Jul 20 2017: (Start) G.f.: 3*x*(7 - 5*x)/(1-x)^3. E.g.f.: 3*x*(x+7)*exp(x). (End) From Amiram Eldar, Feb 26 2022: (Start) Sum_{n>=1} 1/a(n) = 49/360. Sum_{n>=1} (-1)^(n+1)/a(n) = 37/1080. (End) MAPLE A140681:=n->3*n*(n+6); seq(A140681(n), n=0..100); # Wesley Ivan Hurt, Dec 10 2013 MATHEMATICA Table[3n(n+6), {n, 0, 100}] (* Wesley Ivan Hurt, Dec 10 2013 *) LinearRecurrence[{3, -3, 1}, {0, 21, 48}, 50] (* Harvey P. Dale, May 03 2023 *) PROG (PARI) a(n)=3*n*(n+6) \\ Charles R Greathouse IV, Jun 17 2017 CROSSREFS Cf. A028560, A033428, A045944, A140676, A067725, A140677, A140678, A067707, A140679, A140680, A140689, A000217, A005563, A067728, A140091, A212331. Sequence in context: A156966 A146705 A146713 * A262423 A020178 A347372 Adjacent sequences: A140678 A140679 A140680 * A140682 A140683 A140684 KEYWORD nonn,easy AUTHOR Omar E. Pol, May 22 2008 STATUS approved

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Last modified June 4 03:55 EDT 2023. Contains 363118 sequences. (Running on oeis4.)