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Numbers k such that 12*3^k + 1 is prime.
1

%I #21 Aug 27 2022 03:16:53

%S 0,1,2,5,13,14,38,200,248,884,1004,1253,1634,3305,3521,9601,19784,

%T 72697

%N Numbers k such that 12*3^k + 1 is prime.

%C a(19) > 2*10^5. - _Robert Price_, Mar 16 2014

%C All terms are verified primes (i.e., not merely probable primes). - _Robert Price_, Mar 16 2014

%F a(n) = A005537(n+1) - 1. - _Bruno Berselli_, Sep 27 2012

%t Select[Range[4000], PrimeQ[12 * 3^# + 1] &]

%o (Magma) [n: n in [0..4000] | IsPrime(12*3^n + 1)];

%o (PARI) is(n)=ispseudoprime(12*3^n+1) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A003306, A005537-A005539, A056805.

%K nonn,more

%O 1,3

%A _Vincenzo Librandi_, Sep 26 2012

%E a(16)-a(17) from _Vincenzo Librandi_, Sep 30 2012

%E a(18) from _Robert Price_, Mar 16 2014