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A146309
a(n) = indices where primes occurred in A146306.
3
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).
MATHEMATICA
aa = {}; Do[k = Denominator[(n - 6)/(2 n)]; If[PrimeQ[k], AppendTo[aa, n]], {n, 1, 1000}]; aa (*Artur Jasinski*)
KEYWORD
nonn
AUTHOR
Artur Jasinski, Oct 29 2008
STATUS
approved