OFFSET
1,3
COMMENTS
Also, numbers k such that (172*10^k - 1)/9 is prime.
Terms from Kamada.
a(13) > 250000.
LINKS
EXAMPLE
For k=1, R_3 + 8*10^1 = 111 + 80 = 191 which is prime.
MATHEMATICA
Select[Range[0, 250000], PrimeQ[(172*10^#-1)/9 ] &]
PROG
(Magma) [n: n in [0..300] | IsPrime((172*10^n-1) div 9)]; // Vincenzo Librandi, Apr 14 2015
(PARI) for(n=0, 300, if(isprime((172*10^n-1)/9), print1(n, ", "))) \\ Derek Orr, Apr 14 2015
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 13 2015
STATUS
approved