OFFSET
1,3
COMMENTS
Also, numbers k such that (112*10^k - 1)/3 is prime.
Terms from Kamada.
a(25) > 250000.
LINKS
EXAMPLE
For k=2, 3*R_4 + 4*10^2 = 3333 + 400 = 3733 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(112*10^#-1)/3 ] &]
PROG
(PARI) for(n=0, 500, if(isprime((112*10^n-1)/3), print1(n, ", "))) \\ Derek Orr, Apr 14 2015
(Magma) [n: n in [0..300] | IsPrime((112*10^n-1) div 3)]; // Vincenzo Librandi, Apr 15 2015
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 14 2015
STATUS
approved