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A127997 Numbers n such that (22^n - 1)/21 is prime. 9

%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/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[100]],PrimeQ[(22^#-1)/21]&]

%o (PARI) isok(n) = isprime((22^n-1)/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

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Last modified January 22 22:16 EST 2020. Contains 331166 sequences. (Running on oeis4.)