%I
%S 2,5,79,101,359,857,4463,9029,27823
%N Numbers n such that (22^n  1)/21 is prime.
%C 9029 is a term found by Richard Fischer in 2004.  _Alexander Adamchuk_, Feb 11 2007
%C No other terms < 100000.  _Robert Price_, Feb 25 2012
%H H. Dubner, <a href="http://dx.doi.org/10.1090/S00255718199311852439">Generalized repunit primes</a>, Math. Comp., 61 (1993), 927930.
%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)^n1)/k
%t Select[Prime[Range[100]],PrimeQ[(22^#1)/21]&]
%o (PARI) isok(n) = isprime((22^n1)/21); \\ _Michel Marcus_, Mar 13 2016
%K hard,more,nonn
%O 1,1
%A _Alexander Adamchuk_, Feb 11 2007
%E More terms from _Ryan Propper_, Mar 29 2007
%E 27823 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
