OFFSET
1,2
COMMENTS
Also, numbers k such that (14*10^k - 41)/9 is prime.
Terms from Kamada data.
a(10) > 10^5.
Per Kamada link, 211262, 222718, 250336 are also terms, found by Serge Batalov - Michael S. Branicky, Sep 13 2024
LINKS
EXAMPLE
For k=4, 5*R_4 + 10^k - 4 = 5555 + 10000 - 4 = 15551 which is prime.
MATHEMATICA
Select[Range[100000], PrimeQ[(14*10^#-41)/9] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Jun 18 2015
STATUS
approved