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 A216647 a(n) := card{cos((2^(k-1))*Pi/n): k=1,2,...}. 0

%I

%S 2,3,2,4,3,3,4,5,4,4,6,4,7,5,5,6,5,5,10,5,7,7,12,5,11,8,10,6,15,6,6,7,

%T 6,6,13,6,19,11,13,6,11,8,8,8,13,13,24,6,22,12,9,9,27,11,21,7,10,16,

%U 30,7,31,7,7,8,7,7,34,7,23,14,36,7

%N a(n) := card{cos((2^(k-1))*Pi/n): k=1,2,...}.

%C The sequence a(n) is an "even" supplement of the sequence A216066.

%C Does there exists an infinite sets of solutions (in indices n in N) to each of the following three relations: a(n) + a(n+2) > a(n+1), a(n) + a(n+2) = a(n+1), and a(n) + a(n+2) < a(n+1)?

%D R. Witula and D. Slota, Fixed and periodic points of polynomials generated by minimal polynomials of 2cos(2Pi/n), International J. Bifurcation and Chaos, 19 (9) (2009), 3005.

%Y Cf. A216066.

%K nonn

%O 1,1

%A _Roman Witula_, Sep 12 2012

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Last modified March 23 14:17 EDT 2019. Contains 321431 sequences. (Running on oeis4.)