OFFSET
1,2
COMMENTS
Also numbers n such that (4*10^n-13)/9 is prime.
a(13) > 10^5. - Robert Price, Oct 25 2014
LINKS
FORMULA
a(n) = A056661(n) + 1.
EXAMPLE
n=30 means that 444444444444444444444444444443 is prime.
MATHEMATICA
Do[ If[ PrimeQ[ 4(10^n - 1)/9 - 1], Print[n]], {n, 5000}] (* Robert G. Wilson v, Oct 14 2004 *)
Select[Range[500], PrimeQ[FromDigits[PadLeft[{3}, #, 4]]]&] (* The program generates the first 11 terms of the sequence. *) (* Harvey P. Dale, Feb 10 2022 *)
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Labos Elemer, Jul 15 2004
EXTENSIONS
a(12) from Robert Price, Oct 25 2014
STATUS
approved