%I #17 Aug 04 2020 12:16:25
%S 5,3181,61441,91943,121949,221411
%N Numbers n such that (23^n - 1)/22 is prime.
%C No other terms < 100000.
%H H. Lifchitz, <a href="http://www.primenumbers.net/Henri/us/MersFermus.htm">Mersenne and Fermat primes field</a>
%t Select[Prime[Range[100]], PrimeQ[(23^#-1)/22]&]
%o (PARI) is(n)=ispseudoprime((23^n-1)/22) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A028491, A004061, A004062, A004063, A004023, A004064, A016054, A006032, A006033, A006034, A006035, A127995, A127996, A127997, A127998, A127999, A128000, A098438, A128002, A128003, A128004, A128005.
%K hard,nonn,more
%O 1,1
%A _Robert Price_, Jan 20 2012
%E a(5)=121949 corresponds to a probable prime discovered by _Paul Bourdelais_, Oct 19 2017
%E a(6)=221411 corresponds to a probable prime discovered by _Paul Bourdelais_, Aug 04 2020