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A007486
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a(n) = a(n-1)+a(n-2)+a(n-3).
(Formerly M2351)
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1
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1, 3, 4, 8, 15, 27, 50, 92, 169, 311, 572, 1052, 1935, 3559, 6546, 12040, 22145, 40731, 74916, 137792, 253439, 466147, 857378, 1576964, 2900489, 5334831, 9812284, 18047604, 33194719, 61054607, 112296930, 206546256, 379897793, 698740979, 1285185028
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| If A001590 is the Tribonacci series, this might be called the Trucas series after the Lucas series A000032. - Paul Wayper (paulway(AT)mabula.net), Nov 28 2007
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REFERENCES
| N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| Vincenzo Librandi, Table of n, a(n) for n = 1..108
Index to sequences with linear recurrences with constant coefficients, signature (1,1,1).
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FORMULA
| O.g.f.: x*(1+2*x)/(1-x-x^2-x^3). a(n)=A001590(n)+3*A000073(n). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 22 2008]
a(n) = 2*a(n-1) - a(n-4), n>4. [From Vincenzo Librandi, Jun 08 2011]
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MATHEMATICA
| LinearRecurrence[{1, 1, 1}, {1, 3, 4}, 100] (* From Vladimir Joseph Stephan Orlovsky, June 07 2011 *)
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PROG
| (PARI) Vec((x+2*x^2)/(1-x-x^2-x^3)+O(x^99)) \\ Charles R Greathouse IV, Jun 08 2011
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CROSSREFS
| Cf. A001590, A000032, A000045.
Sequence in context: A104370 A033854 A042981 * A027977 A165438 A202025
Adjacent sequences: A007483 A007484 A007485 * A007487 A007488 A007489
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KEYWORD
| nonn,easy
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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