OFFSET
1,2
COMMENTS
Also, numbers k such that (16*10^k - 61)/9 is prime.
Terms from Kamada data.
a(11) > 10^5.
LINKS
EXAMPLE
For k=6, 7*R_6 + 10^k - 6 = 777777 + 10000000 - 6 = 1777771 which is prime.
MATHEMATICA
Select[Range[100000], PrimeQ[(16*10^#-61)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 18 2015
STATUS
approved