%I #16 May 21 2018 03:24:55
%S 4,5,7,13,25,33,41,63,74,80,88,94,96,104,116,144,149,151,154,165,167,
%T 174,183,191,197,208,231,241,262,268,270,290,318,319,361,368,376,390,
%U 394,412,431,434,442,464,489,492,521,529,556,568,574,575,585,589,613,629,639,654,666,667,672,683,684
%N Numbers n such that Phi_28(n) is prime, where Phi is the cyclotomic polynomial.
%H G. C. Greubel, <a href="/A250182/b250182.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[700], PrimeQ[Cyclotomic[28, #]] &] (* _Vincenzo Librandi_, Jan 17 2015 *)
%o (PARI) isok(n) = isprime(polcyclo(28, n)); \\ _Michel Marcus_, Jan 17 2015
%Y Cf. A246392.
%K nonn
%O 1,1
%A _R. J. Mathar_, Jan 09 2015