OFFSET
1,2
COMMENTS
Also, numbers k such that (10^k + 59)/3 is prime.
Terms from Kamada data. Note that Kamada does not recognize k=1 as 23 is a degenerate case of form AAA..ABA.
a(19) > 2.5*10^5.
LINKS
EXAMPLE
For k=3, 3*R_3 + 20 = 333 + 20 = 353 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(10^# + 59)/3] &]
PROG
(PARI) is(n)=ispseudoprime(10^n\3+20) \\ Charles R Greathouse IV, Apr 10 2015
(Magma) [n: n in [0..300] | IsPrime((10^n+59) div 3)]; // Vincenzo Librandi, Apr 11 2015
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 10 2015
STATUS
approved