1,1

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 occurence n in this sequence see A146308.

a(n+5)=A051724(n)

Table[Numerator[(n - 6)/(2 n)], {n, 1, 100}] (*Artur Jasinski*)

A007310, A051724, A146307, A146308

Sequence in context: A137373 A086464 A162298 this_sequence A119788 A059592 A098087

Adjacent sequences: A146303 A146304 A146305 this_sequence A146307 A146308 A146309

sign

Artur Jasinski (grafix(AT)csl.pl), Oct 29 2008