VOOZH about

URL: https://oeis.org/A237251

⇱ A237251 - OEIS

login
A237251
Primes p such that p*2^(p-1)-1 is prime.
0
2, 3, 5, 17, 257, 16487
OFFSET
1,1
COMMENTS
The fifth Fermat prime, 65537, is not in the sequence: 65537*2^65536-1 is composite (per PFGW). - Michael B. Porter, Feb 11 2014
Also 65537*2^65536-1 is divisible by 16267 and 2058772459. - Jeppe Stig Nielsen, Jan 04 2020
PROG
(PARI) isok(p) = isprime(p) && isprime(p*2^(p-1) - 1); \\ Michel Marcus, Feb 06 2014
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Gerasimov Sergey, Feb 05 2014
EXTENSIONS
a(5) from Ralf Stephan, Feb 03 2014
a(6) = A230769(26)+1 appended by Jeppe Stig Nielsen, Jan 04 2020
STATUS
approved