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 A169723 3^(n-1)*(2*3^(n-1)+3)+1. 1
 6, 28, 190, 1540, 13366, 118828, 1065070, 9572500, 86113126, 774900028, 6973745950, 62762650660, 564860667286, 5083736439628, 45753599258830, 411782307236020, 3706040506843846, 33354363786753628, 300189271756259710, 2701703438832768580 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A subsequence of the triangular numbers A000217. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Alice V. Kleeva, Grid for this sequence Alice V. Kleeva, Illustration of initial terms Robert Munafo, Sequence A169720, and two others by Alice V. Kleeva Robert Munafo, Sequence A169720, and two others by Alice V. Kleeva [Cached copy, in pdf format, included with permission] Index entries for linear recurrences with constant coefficients, signature (13,-39,27). FORMULA G.f.: x*(-6+50*x-60*x^2)/((x-1)*(3*x-1)*(9*x-1)). - Vincenzo Librandi, Dec 03 2012 a(n) = 13*a(n-1)-39*a(n-2)+27*a(n-3). - Vincenzo Librandi, Dec 03 2012 a(n) = 2*9^(n-1)+3^n+1. - Bruno Berselli, Dec 05 2012 MATHEMATICA LinearRecurrence[{13, -39, 27}, {6, 28, 190}, 50]  (* or *) CoefficientList[Series[(-6 + 50 x - 60 x^2)/((x - 1) (3 x - 1) (9 x - 1)), {x, 0, 20}], x] (* Vincenzo Librandi, Dec 03 2012 *) PROG (MAGMA) I:=[6, 28, 190]; [n le 3 select I[n] else 13*Self(n-1)-39*Self(n-2)+27*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Dec 03 2012 CROSSREFS Cf. A169720-A169727, A100702. Sequence in context: A278015 A338810 A345002 * A052395 A034660 A347770 Adjacent sequences:  A169720 A169721 A169722 * A169724 A169725 A169726 KEYWORD nonn,easy AUTHOR Alice V. Kleeva (alice27353(AT)gmail.com), Jan 19 2010 STATUS approved

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Last modified May 22 17:42 EDT 2022. Contains 353957 sequences. (Running on oeis4.)