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A050556 Numbers k such that 61*2^k-1 is prime. 0
3, 5, 9, 13, 17, 19, 25, 39, 63, 67, 75, 119, 147, 225, 419, 715, 895, 1025, 1103, 1179, 1345, 1829, 3855, 4159, 4493, 6039, 7799, 9073, 10543, 12883, 23807, 23957, 36163, 44047, 51975, 65573, 79393, 79949, 81987, 86349, 384287, 499175, 762417, 971585 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

499175 is also a member. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

LINKS

Table of n, a(n) for n=1..44.

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.

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

MATHEMATICA

Select[Range[1000], PrimeQ[61*2^# - 1] & ] (* Robert Price, Dec 22 2018 *)

PROG

(PARI) is(n)=ispseudoprime(61*2^n-1) \\ Charles R Greathouse IV, Jun 13 2017

CROSSREFS

Sequence in context: A181557 A286058 A076052 * A138008 A063954 A123509

Adjacent sequences:  A050553 A050554 A050555 * A050557 A050558 A050559

KEYWORD

hard,nonn,more

AUTHOR

N. J. A. Sloane, Dec 29 1999

EXTENSIONS

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

a(42)-a(44) from the Wilfrid Keller link by Robert Price, Dec 22 2018

STATUS

approved

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Last modified June 18 14:52 EDT 2019. Contains 324213 sequences. (Running on oeis4.)