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 A146306 a(n) = numerator of (n-6)/(2n) 4
 -5, -1, -1, -1, -1, 0, 1, 1, 1, 1, 5, 1, 7, 2, 3, 5, 11, 1, 13, 7, 5, 4, 17, 3, 19, 5, 7, 11, 23, 2, 25, 13, 9, 7, 29, 5, 31, 8, 11, 17, 35, 3, 37, 19, 13, 10, 41, 7, 43, 11, 15, 23, 47, 4, 49, 25, 17, 13, 53, 9, 55, 14, 19, 29, 59, 5, 61, 31, 21, 16, 65, 11, 67, 17, 23, 35, 71, 6, 73, 37 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For denominators see A146307. General formula (*Artur Jasinski*): 2 Cos[2*Pi/n] = Hypergeometric2F1[(n-6)/(2n),(n+6)/(2n),1/2,3/4] = Hypergeometric2F1[a(n)/A146307(n),a(n+12)/A146307(n),1/2,3/4]. 2 Cos[2*Pi/n] is root of polynomial of degree = EulerPhi[n]/2 = A000010(n)/2 = A023022(n). Records in this sequence are congruent to 1 or 5 mod 6 (see A007310). First occurrence n in this sequence see A146308. LINKS FORMULA a(n+5)=A051724(n) MATHEMATICA Table[Numerator[(n - 6)/(2 n)], {n, 1, 100}] (*Artur Jasinski*) CROSSREFS Sequence in context: A162298 A196755 A199510 * A336697 A326073 A257098 Adjacent sequences:  A146303 A146304 A146305 * A146307 A146308 A146309 KEYWORD sign AUTHOR Artur Jasinski, Oct 29 2008 STATUS approved

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Last modified July 24 06:56 EDT 2021. Contains 346273 sequences. (Running on oeis4.)