OFFSET
1,1
COMMENTS
Also, numbers k such that (673*10^k - 7)/9 is prime.
Terms from Kamada.
a(9) > 30000.
LINKS
EXAMPLE
For k=5, 7*R_7 - 3*10^5 = 7777777 - 300000 = 7477777 which is prime.
MATHEMATICA
Select[Range[0, 30000], PrimeQ[(673*10^#-7)/9 ] &]
PROG
(Magma) [n: n in [0..400] | IsPrime((673*10^n-7) div 9)]; // Vincenzo Librandi, Apr 15 2015
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 14 2015
STATUS
approved