%I #9 Jul 31 2019 09:05:38
%S 5,7,2707,163193
%N Numbers k such that (37^k + 1)/38 is prime.
%C Larger terms correspond to probable primes.
%H P. Bourdelais, <a href="https://listserv.nodak.edu/cgi-bin/wa.exe?A2=NMBRTHRY;417ab0d6.0906">A Generalized Repunit Conjecture</a>
%t Do[p=Prime[n]; If[PrimeQ[(37^p + 1)/38], Print[p]], {n, 1, 1000000}]
%o (PARI) is(n)=ispseudoprime((37^n+1)/38)
%K nonn,hard,more
%O 1,1
%A _Paul Bourdelais_, Jul 29 2019