%I #13 Jun 13 2017 13:46:16

%S 349,631,4493,16633,36341

%N Numbers n such that (39^n - 1)/38 is prime.

%H Harvey Dubner, <a href="http://dx.doi.org/10.1090/S0025-5718-1993-1185243-9">Generalized repunit primes</a>, Math. Comp., 61 (1993), 927-930.

%H Henri Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a>

%t Select[Prime[Range[100000]], PrimeQ[(39^#-1)/38]&]

%o (PARI) is(n)=ispseudoprime((39^n-1)/38) \\ _Charles R Greathouse IV_, Jun 13 2017

%Y Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127995, A127996, A127997, A127998, A127999, A098438, A128002, A128003, A128004, A128005.

%K hard,more,nonn

%O 1,1

%A _Robert Price_, Apr 04 2012