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A268061
Numbers k such that 7*8^k - 1 is prime.
4
3, 7, 15, 59, 6127, 8703, 11619, 23403, 124299
OFFSET
1,1
COMMENTS
a(10) > 2*10^5.
Terms are A001771(n)/3 that are integers.
REFERENCES
R. K. Guy, Unsolved Problems in Theory of Numbers, Section A3.
MATHEMATICA
Select[Range[0, 200000], PrimeQ[7*8^# - 1] &]
PROG
(PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*8^n-1), print1(n, ", "))) \\ Altug Alkan, Jan 25 2016
CROSSREFS
Cf. similar sequences of the form k*(k+1)^n-1: A003307 (k=2), ... (k=3), A046865 (k=4), A079906 (k=5), A046866 (k=6), this sequence (k=7), ... (k=8), A056725 (k=9), A046867 (k=10), A079907 (k=11).
Sequence in context: A146448 A192169 A290470 * A298358 A023370 A181071
KEYWORD
nonn,hard,more
AUTHOR
Robert Price, Jan 25 2016
STATUS
approved