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 A019481 a(n) = 3*a(n-1) + a(n-2) - 2*a(n-3) (agrees with A019480 for n <= 19 only). 4
 4, 12, 37, 115, 358, 1115, 3473, 10818, 33697, 104963, 326950, 1018419, 3172281, 9881362, 30779529, 95875387, 298642966, 930245227, 2897627873, 9025842914, 28114666161, 87574585651, 272786737286, 849705465187, 2646753961545, 8244393875250 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 REFERENCES R. K. Guy, personal communication. LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (3,1,-2) FORMULA From R. J. Mathar, Aug 22 2008: (Start) O.g.f.: (4 - 3*x^2)/(1 - 3*x - x^2 + 2*x^3). a(n) = 4*A100058(n) - 3*A100058(n-2). (End) MATHEMATICA LinearRecurrence[{3, 1, -2}, {4, 12, 37}, 30] (* Harvey P. Dale, Jan 17 2017 *) PROG (MAGMA) I:=[4, 12, 37]; [n le 3 select I[n] else 3*Self(n-1)+Self(n-2)-2*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Jan 18 2017 CROSSREFS Sequence in context: A033130 A196918 A099098 * A019480 A192907 A280891 Adjacent sequences:  A019478 A019479 A019480 * A019482 A019483 A019484 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified March 29 21:32 EDT 2020. Contains 333117 sequences. (Running on oeis4.)