OFFSET
1,3
COMMENTS
Also numbers k such that (4*10^(k+1)+23)/9 is prime.
a(13) > 10^5. - Robert Price, Nov 30 2014
LINKS
FORMULA
a(n) = A099413(n+1)-1. - Robert Price, Nov 30 2014
MATHEMATICA
Do[ If[ PrimeQ[40*(10^n - 1)/9 + 7], Print[n]], {n, 0, 5000}]
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
EXTENSIONS
a(10)-a(12) derived from A099413 by Robert Price, Nov 30 2014
STATUS
approved