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A019481
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a(n) = 3*a(n-1) + a(n-2) - 2*a(n-3) (agrees with A019480 for n <= 19 only).
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4
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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
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refs;
listen;
history;
text;
internal format)
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OFFSET
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0,1
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REFERENCES
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R. K. Guy, personal communication.
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LINKS
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FORMULA
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O.g.f.: (4 - 3*x^2)/(1 - 3*x - x^2 + 2*x^3).
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MATHEMATICA
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LinearRecurrence[{3, 1, -2}, {4, 12, 37}, 30] (* Harvey P. Dale, Jan 17 2017 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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