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%I #16 Oct 30 2017 03:52:36
%S 139,173,547,829,2087,2719,3109,10159,56543,80599
%N Numbers n such that (30^n+1)/31 is a prime.
%C Some of the larger terms may only correspond to probable primes.
%C a(11) > 10^5. - _Robert Price_, Jul 10 2013
%H H. Dubner and T. Granlund, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7.
%H H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a>
%t Select[Range[3000], PrimeQ[(30^# + 1) / 31] &] (* _Vincenzo Librandi_, Oct 29 2017 *)
%o (PARI) isok(n) = (denominator(p=(30^n+1)/31)==1) && isprime(p); \\ _Michel Marcus_, Oct 29 2017
%Y Cf. A071381.
%K nonn,more
%O 1,1
%A _Rick L. Shepherd_, May 22 2002
%E a(8) from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
%E a(9)-a(10) from _Robert Price_, Jul 10 2013