OFFSET
1,1
COMMENTS
Also, numbers k such that (68*10^k + 13)/9 is prime.
Terms from Kamada data.
a(20) > 10^5.
LINKS
EXAMPLE
For k=2, 5*R_2 + 7*10^k + 2 = 55 + 700 + 2 = 757 which is prime.
MATHEMATICA
Select[Range[0, 100000], PrimeQ[(68*10^#+13)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 18 2015
STATUS
approved