OFFSET
1,1
COMMENTS
Also, numbers k such that 99*10^k - 1 is prime.
Terms from Kamada.
LINKS
EXAMPLE
For k=3, 9*R_5 - 10^3 = 99999 - 1000 = 98999 which is prime.
MATHEMATICA
Select[Range[0, 280000], PrimeQ[99*10^#-1 ] &]
PROG
(Magma) [n: n in [0..300] | IsPrime(99*10^n-1)]; // Vincenzo Librandi, Apr 15 2015
CROSSREFS
KEYWORD
more,hard,nonn
AUTHOR
Robert Price, Apr 14 2015
EXTENSIONS
a(21) from Predrag Kurtovic, May 24 2015
STATUS
approved