A239741 Numbers k such that prime(k) * 2^k - 1 is prime.

1, 2, 11, 24, 28, 92, 166, 191, 220, 587, 677, 964, 988, 1840, 2664, 3604, 6079, 6640, 8817, 33647, 34308, 39882, 44055, 47050, 64100, 103313, 223439, 225921

Offset

1,2

Comments

The PFGW program has been used to certify all the terms up to a(28), using a deterministic test which exploits the factorization of a(n)+1.

a(29) > 290000.

Links

Table of n, a(n) for n=1..28.

Mathematica

Select[Range[1000], PrimeQ[Prime[#]*2^# - 1] &]

Prog

(Magma) [n: n in [0..1000] | IsPrime(NthPrime(n)*2^n-1)]; // Vincenzo Librandi, Dec 24 2015
(PARI) is(n, p=prime(n))=ispseudoprime(p<<n-1) \\ Charles R Greathouse IV, Jun 06 2017

Crossrefs

Cf. A239742.

Sequence in context: A115374 A078699 A291679 * A042347 A193245 A041803

Adjacent sequences: A239738 A239739 A239740 * A239742 A239743 A239744

Keyword

nonn,more

Author

Giovanni Resta, Mar 26 2014

Status

approved