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%I #12 Jun 12 2017 19:02:50
%S 1,3,4,31,33,76,196,319,405,591,2028,2140,4039,5745,16629,18061,20265,
%T 54129,119712
%N Numbers n such that 7*3^n + 2 is prime.
%C a(20) > 2*10^5. - _Robert Price_, May 12 2015
%t Do[ If[ PrimeQ[ 7*3^n + 2 ], Print[ n ] ], {n, 1, 2500} ]
%t Select[Range[0, 10000], PrimeQ[(7*3^# + 2)] &] (* _Vincenzo Librandi_, Sep 29 2012 *)
%o (PARI) is(n)=ispseudoprime(7*3^n+2) \\ _Charles R Greathouse IV_, Jun 12 2017
%K nonn
%O 1,2
%A _Robert G. Wilson v_, Dec 26 2000
%E a(13)-a(14) from _Vincenzo Librandi_, Sep 29 2012
%E a(15)-a(19) from _Robert Price_, May 12 2015