|
%I #26 Jan 04 2020 15:05:00
%S 2,3,5,17,257,16487
%N Primes p such that p*2^(p-1)-1 is prime.
%C The fifth Fermat prime, 65537, is not in the sequence: 65537*2^65536-1 is composite (per PFGW). - _Michael B. Porter_, Feb 11 2014
%C Also 65537*2^65536-1 is divisible by 16267 and 2058772459. - _Jeppe Stig Nielsen_, Jan 04 2020
%o (PARI) isok(p) = isprime(p) && isprime(p*2^(p-1) - 1); \\ _Michel Marcus_, Feb 06 2014
%Y Cf. A019434, A092506, A230769, A236752.
%K nonn,more,hard
%O 1,1
%A _Gerasimov Sergey_, Feb 05 2014
%E a(5) from _Ralf Stephan_, Feb 03 2014
%E a(6) = A230769(26)+1 appended by _Jeppe Stig Nielsen_, Jan 04 2020
|
