OFFSET
1,2
COMMENTS
Also, numbers k such that (10^k + 539)/9 is prime.
Terms from Kamada data. Note that Kamada does not recognize k=1 as 61 is a degenerate case of form AAA..ABA.
a(18) > 2.5*10^5.
LINKS
EXAMPLE
For k=5, R_5 + 60 = 11111 + 60 = 11171 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 539)/9] &]
PROG
(Magma) [n: n in [1..400] | IsPrime((10^n+539) div 9)]; // Vincenzo Librandi, Apr 10 2015
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 09 2015
STATUS
approved