This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A146309 #4 Jul 22 2014 15:06:47
%S A146309 1,3,10,14,18,22,26,30,34,38,42,46,58,62,66,74,78,82,86,94,102,106,
%T A146309 114,118,122,134,138,142,146,158,166,174,178,186,194,202,206,214,218,
%U A146309 222,226,246,254,258,262,274,278,282,298,302,314,318,326,334,346,354,358
%N A146309 a(n) = indices where primes occurred in A146306.
%C A146309 General formula (*Artur Jasinski*):
%C A146309 2 Cos[2*Pi/n] = Hypergeometric2F1[(n-6)/(2n),(n+6)/(2n),1/2,3/4] =
%C A146309 Hypergeometric2F1[A146306(n)/A146307(n),A146306(n+12)/A146307(n),1/2,3/4].
%C A146309 2 Cos[2*Pi/n] is root of polynomial of degree = EulerPhi[n]/2 = A000010(n)/2 = A023022(n).
%t A146309 aa = {}; Do[k = Denominator[(n - 6)/(2 n)]; If[PrimeQ[k], AppendTo[aa, n]], {n, 1, 1000}]; aa (*Artur Jasinski*)
%Y A146309 A007310, A051724, A146306, A146307, A146308.
%K A146309 nonn
%O A146309 0,2
%A A146309 _Artur Jasinski_, Oct 29 2008