OFFSET
1,2
COMMENTS
Also numbers k such that (46*10^k - 1)/9 is prime.
a(18) > 10^5. - Robert Price, Dec 08 2014
LINKS
MATHEMATICA
Do[ If[ PrimeQ[ 5*10^n + (10^n-1)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 11 2000
EXTENSIONS
a(11) from Hugo Pfoertner, Oct 19 2004
a(12)-a(17) from Robert Price, Dec 08 2014
STATUS
approved