OFFSET
1,1
COMMENTS
Also numbers k such that (5*10^(k+1)-41)/9 is prime.
a(4) > 10^5. - Robert Price, Nov 16 2014
LINKS
FORMULA
a(n) = A099415(n) - 1. - Robert Price, Nov 16 2014
MATHEMATICA
Do[ If[ PrimeQ[50*(10^n - 1)/9 + 1], Print[n]], {n, 15000}]
CROSSREFS
KEYWORD
hard,nonn,bref,more
AUTHOR
Robert G. Wilson v, Aug 10 2000
STATUS
approved