OFFSET
1,2
COMMENTS
Also, numbers k such that (10^k + 629)/9 is prime.
Terms from Kamada data. Note that Kamada does not recognize k=1 as 81 is a degenerate case of form AAA..ABA.
a(20) > 2.5*10^5.
LINKS
EXAMPLE
For k=3, R_3 + 70 = 111 + 70 = 181 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 629)/9] &]
PROG
(Magma) [n: n in [1..350] | IsPrime((10^n+629) div 9)]; // Vincenzo Librandi, Apr 10 2015
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Robert Price, Apr 09 2015
STATUS
approved