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%I #12 May 19 2018 02:02:49
%S 2,6,8,11,23,35,41,49,58,65,85,88,97,107,111,139,144,161,170,197,214,
%T 217,223,230,238,247,274,298,301,323,382,389,393,398,403,427,445,452,
%U 473,480,497,511,561,575,595,601,604,606,615,629,651,652,680,685,702,725,762,770,774,781,805,814,912,918,942,987,1030
%N Numbers n such that Phi(42,n) is prime, where Phi is the cyclotomic polynomial.
%H G. C. Greubel, <a href="/A250190/b250190.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[1100], PrimeQ[Cyclotomic[42, #]] &] (* _Vincenzo Librandi_, Jan 16 2015 *)
%o (PARI) {is(n)=isprime(polcyclo(42,n))};
%o for(n=1,1000, if(is(n)==1, print1(n, ", "))) \\ _G. C. Greubel_, May 18 2018
%Y Cf. A246392.
%K nonn
%O 1,1
%A _R. J. Mathar_, Jan 12 2015