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A050539 Numbers k such that 27*2^k-1 is prime. 5
1, 2, 4, 5, 8, 10, 14, 28, 37, 38, 70, 121, 122, 160, 170, 253, 329, 362, 454, 485, 500, 574, 892, 962, 1213, 1580, 2642, 2708, 4505, 8152, 11858, 13300, 15041, 16118, 16778, 19069, 22769, 29020, 30298, 30377, 35942, 42817, 42869, 62024, 74629, 90449, 91042, 117901, 128594, 143330, 152530, 157898, 175852, 340682, 444622, 627794, 729314, 777992, 1108214, 1163629, 1253870 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

3855094, 4542344 and 4583717 are also in the sequence. - Felix Fröhlich, Sep 19 2014

LINKS

Table of n, a(n) for n=1..61.

Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300

Wilfrid Keller, List of primes k.2^n - 1 for k < 300

Kosmaj, Riesel list k<300.

PrimeGrid, Announcement of n=3855094 , Announcement of n=4542344, Announcement of n=4583717 - Felix Fröhlich, Sep 19 2014

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

MATHEMATICA

For[n = 1, n <= 10000, n++, If[PrimeQ[27*2^n - 1], Print[n]]] (* Wesley Ivan Hurt, May 19 2014 *)

Select[Range[1000], PrimeQ[27*2^# - 1] & ] (* Robert Price, Dec 22 2018 *)

PROG

(PARI) a(n)=if(ispseudoprime(27*2^n-1), print1(n, ", ")) \\ Felix Fröhlich, Sep 19 2014

CROSSREFS

Cf. A032363 = 27*2^n+1 is prime.

Sequence in context: A163295 A101274 A080222 * A277101 A039895 A300351

Adjacent sequences: A050536 A050537 A050538 * A050540 A050541 A050542

KEYWORD

hard,nonn

AUTHOR

N. J. A. Sloane, Dec 29 1999

EXTENSIONS

More terms from Hugo Pfoertner, Aug 17 2004

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(59)-a(61) from the Wilfrid Keller link by Robert Price, Dec 22 2018

STATUS

approved

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Last modified December 9 23:05 EST 2022. Contains 358710 sequences. (Running on oeis4.)