%I
%S 1,2,3,7,12,17,19,51,65,550,1460,1641,7035,18002,20963,21163,42563,
%T 94906,148048
%N Numbers n such that 15^n  2 is a prime.
%C a(20) > 2*10^5.  _Robert Price_, Jun 23 2015
%t Do[ f = 15^n  2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n,1,1000} ]
%t Do[If[PrimeQ[15^n  2], Print[n]], {n, 10^4}] (* _Ryan Propper_, Jun 06 2007 *)
%Y Cf. A084714 = smallest prime of the form (2n1)^k  2, or 0 if no such number exists. Cf. A128472 = smallest prime of the form (2n1)^k  2 for k>(2n1), or 0 if no such number exists. Cf. A014224, A109080, A090669, A128455, A128457, A128459, A128460, A128461.
%K hard,more,nonn
%O 1,2
%A _Alexander Adamchuk_, Mar 14 2007
%E 550 from _Stefan Steinerberger_, May 05 2007
%E 3 more terms from _Ryan Propper_, Jun 06 2007
%E a(14)a(19) from _Robert Price_, Jun 23 2015
