OFFSET
1,2
COMMENTS
Even exponents can give at most semiprimes (see A181490). - Jeppe Stig Nielsen, Jun 08 2023
REFERENCES
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
Jeppe Stig Nielsen, Table of n, a(n) for n = 1..48
Wilfrid Keller, List of primes k.2^n - 1 for k < 300
C. K. Caldwell, The Prime Pages
The Prime Pages, Search output for 9*2^k - 1
Prime-Wiki, Riesel primes of the form 9*2^n - 1
Kosmaj, Riesel list k<300.
H. Riesel, Lucasian criteria for the primality of N=h.2^n-1, Math. Comp., 23 (1969), 869-875.
MATHEMATICA
b=9; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 22}] (* Lei Zhou, Nov 08 2013 *)
Select[Range[3400], PrimeQ[9*2^#-1]&] (* The program generates the first 22 terms of the sequence. To generate more, increase the Range constant, but the program may take a long time to run. *) (* Harvey P. Dale, Sep 01 2020 *)
PROG
(PARI) is(n)=ispseudoprime(9*2^n-1) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
hard,nonn,nice
AUTHOR
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(42)-a(43) communicated by Jeppe Stig Nielsen, Jun 08 2023
STATUS
approved