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A239741 Numbers n such that prime(n) * 2^n - 1 is prime. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 23 03:26 EDT 2019. Contains 322380 sequences. (Running on oeis4.)