OFFSET
1,2
COMMENTS
Also, numbers k such that (106*10^k - 1)/3 is prime.
Terms from Kamada.
a(31) > 250000.
LINKS
EXAMPLE
For k=4, 3*R_6 + 2*10^4 = 333333 + 20000 = 353333 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(106*10^#-1)/3 ] &]
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 14 2015
STATUS
approved