OFFSET
1,2
COMMENTS
Also numbers k such that (7*10^k - 43)/9 is prime.
a(18) > 10^5. - Robert Price, Oct 19 2014
LINKS
FORMULA
a(n) = A056689(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[ 7(10^n - 1)/9 - 4], Print[n]], {n, 0, 5000}]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert G. Wilson v, Oct 14 2004
EXTENSIONS
a(13)-a(17) from Robert Price, Oct 19 2014
STATUS
approved