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A002236 Numbers n such that 9*2^n - 1 is prime.
(Formerly M2634 N1045)
7
1, 3, 7, 13, 15, 21, 43, 63, 99, 109, 159, 211, 309, 343, 415, 469, 781, 871, 939, 1551, 3115, 3349, 5589, 5815, 5893, 7939, 8007, 11547, 12495, 22555, 23647, 35647, 83415, 103059, 184999, 275859, 384243, 484975, 503893, 828709, 1010277 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

H. Riesel, Lucasian criteria for the primality of N=h.2^n-1, Math. Comp., 23 (1969), 869-875.

H. Riesel, "Prime numbers and computer methods for factorization," Progress in Mathematics, Vol. 57, Birkhauser, Boston, 1985, Chap. 4, see pp. 381-384.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Table of n, a(n) for n=1..41.

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

C. K. Caldwell, The Prime Pages

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

b=9; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 22}] (* Lei Zhou, Nov 08 2013 *)

PROG

(PARI) is(n)=ispseudoprime(9*2^n-1) \\ Charles R Greathouse IV, Feb 17 2017

CROSSREFS

Cf. A050524.

Sequence in context: A092734 A209839 A192854 * A255682 A080565 A164344

Adjacent sequences:  A002233 A002234 A002235 * A002237 A002238 A002239

KEYWORD

hard,nonn,nice

AUTHOR

N. J. A. Sloane

EXTENSIONS

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

STATUS

approved

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Last modified September 17 08:31 EDT 2019. Contains 327127 sequences. (Running on oeis4.)