OFFSET
1,2
COMMENTS
Also, numbers k such that (13*10^k - 31)/9 is prime.
Terms from Kamada data.
a(7) > 10^5.
LINKS
EXAMPLE
For k=6, 4*R_6 + 10^k - 3 = 444444 + 1000000 - 3 = 1444441 which is prime.
MATHEMATICA
Select[Range[100000], PrimeQ[(13*10^#-31)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 18 2015
STATUS
approved