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.
LINKS
H. C. Williams, The primality of certain integers of the form 2Ar^n - 1, Acta Arith. 39 (1981), 7-17.
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
KEYWORD
nonn,hard,more
AUTHOR
Robert Price, Jan 25 2016
STATUS
approved