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A050856
Numbers k such that 209*2^k-1 is prime.
0
4, 8, 16, 28, 40, 52, 80, 148, 328, 8464, 11704, 52372, 60172, 675232, 692692, 921484
OFFSET
1,1
MATHEMATICA
Select[Range[1000], PrimeQ[209*2^# - 1] & ] (* Robert Price, Dec 29 2018 *)
PROG
(PARI) is(n)=ispseudoprime(209*2^n-1) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
Sequence in context: A273080 A020193 A176817 * A271649 A128441 A009861
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(16) from the Wilfrid Keller link by Robert Price, Dec 29 2018
STATUS
approved