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%I #7 Feb 17 2017 16:43:22
%S 1,2,3,5,7,8,10,12,13,17,20,22,27,28,30,32,35,38,43,45,52,55,58,60,62,
%T 63,65,68,70,73,75,77,82,83,87,93,97,100,102,115,120,122,130,132,143,
%U 150,153,168,173,177,187,193,197,200,207,208,210,212,220,222,223,225
%N Numbers n such that 6n^2 - 1 is prime.
%t p = 6; a = {}; Do[k = p x^2 - 1; If[PrimeQ[k], AppendTo[a, x]], {x, 1, 1000}]; a
%t Select[Range[250],PrimeQ[6#^2-1]&] (* _Harvey P. Dale_, Apr 22 2012 *)
%o (PARI) is(n)=isprime(6*n^2-1) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y Cf. A090686.
%K nonn
%O 1,2
%A _Artur Jasinski_, Sep 02 2008