A146309 a(n) = indices where primes occurred in A146306.

1, 3, 10, 14, 18, 22, 26, 30, 34, 38, 42, 46, 58, 62, 66, 74, 78, 82, 86, 94, 102, 106, 114, 118, 122, 134, 138, 142, 146, 158, 166, 174, 178, 186, 194, 202, 206, 214, 218, 222, 226, 246, 254, 258, 262, 274, 278, 282, 298, 302, 314, 318, 326, 334, 346, 354, 358

Offset

0,2

Comments

General formula (*Artur Jasinski*):

2 Cos[2*Pi/n] = Hypergeometric2F1[(n-6)/(2n),(n+6)/(2n),1/2,3/4] =

Hypergeometric2F1[A146306(n)/A146307(n),A146306(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).

Links

Table of n, a(n) for n=0..56.

Mathematica

aa = {}; Do[k = Denominator[(n - 6)/(2 n)]; If[PrimeQ[k], AppendTo[aa, n]], {n, 1, 1000}]; aa (*Artur Jasinski*)

Crossrefs

A007310, A051724, A146306, A146307, A146308.

Sequence in context: A316672 A288993 A190706 * A288169 A283867 A085726

Adjacent sequences: A146306 A146307 A146308 * A146310 A146311 A146312

Keyword

nonn

Author

Artur Jasinski, Oct 29 2008

Status

approved