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%I #11 Mar 14 2016 03:31:30
%S 3,83,269,409,1759,11731
%N Numbers n such that (41^n - 1)/40 is prime.
%C a(7) > 10^5. - _Robert Price_, Mar 22 2014
%H H. 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 H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a>
%H <a href="/index/Pri#primepop">Index to primes in various ranges</a>, form ((k+1)^n-1)/k
%t Select[Prime[Range[100000]], PrimeQ[(41^#-1)/40]&]
%o (PARI) isok(n) = isprime((41^n-1)/40); \\ _Michel Marcus_, Mar 13 2016
%K hard,more,nonn
%O 1,1
%A _Robert Price_, Mar 22 2014
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