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A239909
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Arises from a construction of equiangular lines in complex space of dimension 2.
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1
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1, 1, 2, 3, 5, 9, 15, 26, 45, 77, 133, 229, 394, 679, 1169, 2013, 3467, 5970, 10281, 17705, 30489, 52505, 90418, 155707, 268141, 461761, 795191, 1369386, 2358197, 4061013, 6993405, 12043229, 20739450, 35715071, 61504345, 105915637, 182395603, 314100514
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OFFSET
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1,3
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LINKS
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FORMULA
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G.f.: x*(1-x^3)/(x^4-x^3-x^2-x+1).
a(n) = a(n-1) + a(n-2) + a(n-3) - a(n-4) for n>4.
a(n) = a(n-1) + 2*a(n-3) + A116732(n-5) for n>4. (End)
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MATHEMATICA
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LinearRecurrence[{1, 1, 1, -1}, {1, 1, 2, 3}, 40] (* or *) CoefficientList[Series[(1 - x^3)/(x^4 - x^3 - x^2 - x + 1), {x, 0, 100}], x] (* Vincenzo Librandi, Apr 09 2014 *)
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PROG
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(Magma) I:=[1, 1, 2, 3]; [n le 4 select I[n] else Self(n-1)+Self(n-2)+Self(n-3)-Self(n-4): n in [1..50]];
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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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