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A020992
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a(n)=a(n-1)+a(n-2)+a(n-3).
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3
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0, 2, 1, 3, 6, 10, 19, 35, 64, 118, 217, 399, 734, 1350, 2483, 4567, 8400, 15450, 28417, 52267, 96134, 176818, 325219, 598171, 1100208, 2023598, 3721977, 6845783, 12591358, 23159118, 42596259, 78346735, 144102112, 265045106, 487493953, 896641171, 1649180230
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Tribonacci sequence beginning 0, 2, 1.
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FORMULA
| G.f.: x*(2-x)/(1-x-x^2-x^3).
a(n)=2*A000073(n+1)-A000073(n). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Aug 22 2008]
a(n) = 2*a(n-1) - a(n-4), n>3. [From Vincenzo Librandi, Jun 08 2011]
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MATHEMATICA
| LinearRecurrence[{1, 1, 1}, {0, 2, 1}, 100] (* From Vladimir Joseph Stephan Orlovsky, June 07 2011 *)
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CROSSREFS
| Cf. A000032, A001590.
Sequence in context: A024866 A076058 A098124 * A025110 A075346 A104529
Adjacent sequences: A020989 A020990 A020991 * A020993 A020994 A020995
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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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