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A050566
Numbers n such that 81*2^n-1 is prime.
4
3, 5, 11, 17, 21, 27, 81, 101, 107, 327, 383, 387, 941, 1665, 3515, 4007, 4727, 7137, 16257, 16833, 21243, 24239, 35435, 59925, 91673, 153455, 165341, 183167, 190349, 240743, 253385, 308325, 741917
OFFSET
1,1
MATHEMATICA
b=81; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 17}]
PROG
(PARI) is(n)=ispseudoprime(81*2^n-1) \\ Charles R Greathouse IV, Feb 20 2017
CROSSREFS
Sequence in context: A141165 A220954 A155937 * A032382 A167921 A216366
KEYWORD
hard,nonn
AUTHOR
N. J. A. Sloane, Dec 29 1999
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
Lei Zhou, Nov 08 2013, added a Mathematica program for small elements.
STATUS
approved