OFFSET
1,1
COMMENTS
Also, numbers k such that (103*10^k - 1)/3 is prime.
Terms from Kamada.
a(27) > 250000.
LINKS
EXAMPLE
For k=4, 3*R_6 + 10^4 = 333333 + 10000 = 343333 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(103*10^#-1)/3 ] &]
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 14 2015
STATUS
approved