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A237251 Primes p such that p*2^(p-1)-1 is prime. 0
2, 3, 5, 17, 257, 16487 (list; graph; refs; listen; history; text; internal format)
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

LINKS

Table of n, a(n) for n=1..6.

PROG

(PARI) isok(p) = isprime(p) && isprime(p*2^(p-1) - 1); \\ Michel Marcus, Feb 06 2014

CROSSREFS

Cf. A019434, A092506, A230769, A236752.

Sequence in context: A087911 A265426 A099936 * A275584 A092506 A275159

Adjacent sequences:  A237248 A237249 A237250 * A237252 A237253 A237254

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

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Last modified February 28 11:08 EST 2020. Contains 332323 sequences. (Running on oeis4.)