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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 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 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.)