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 A239909 Arises from a construction of equiangular lines in complex space of dimension 2. 1
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 G. McConnell, Some non-standard ways to generate SIC-POVMs in dimensions 2 and 3, arXiiv preprint arXiv:1402.7330, 2014, p. 4. Index entries for linear recurrences with constant coefficients, signature (1,1,1,-1). FORMULA From Vincenzo Librandi Apr 09 2014: (Start) 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) MATHEMATICA 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 *) PROG (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]]; CROSSREFS Cf. A116732. Sequence in context: A018157 A228644 A003065 * A185648 A228645 A185649 Adjacent sequences:  A239906 A239907 A239908 * A239910 A239911 A239912 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Apr 09 2014 STATUS approved

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Last modified March 25 15:02 EDT 2019. Contains 321470 sequences. (Running on oeis4.)