OFFSET
1,2
COMMENTS
Numbers of this form divide 10^(3k)+8.
a(16) > 10360. - Robert G. Wilson v, Jan 12 2018
a(17) > 50000. - Robert Price, Apr 15 2018
EXAMPLE
7, 8331667, 833316667, and 833333316666667 are prime, while 817=19*43, 83167=7*109^2, and 83333166667=97*26209*32779.
MATHEMATICA
Select[Range[1500], PrimeQ[(10^(2 #) - 2 (10^#) + 4)/12] &] (* Michael De Vlieger, Dec 30 2017 *)
PROG
(PARI) isok(k) = isprime((10^(2*k) - 2*(10^k) + 4)/12); \\ Michel Marcus, Dec 30 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Patrick A. Thomas, Dec 30 2017
EXTENSIONS
a(10) from Michel Marcus, Dec 30 2017
a(11)-a(13) from Michael De Vlieger, Dec 30 2017
a(14)-a(15) from Robert G. Wilson v, Jan 08 2018
a(16) from Robert Price, Apr 15 2018
STATUS
approved