OFFSET
1,1
COMMENTS
Primes of the form (9*10^n - 27)/9. - Vincenzo Librandi, Nov 16 2010
Also primes of the form 9*R_n - 2, where R_n is the repunit (A002275) of length n.
The next term has 140 digits.
LINKS
MATHEMATICA
Do[If[PrimeQ[10^n - 3], Print[10^n - 3]], {n, 100}] (* Farideh Firoozbakht, Nov 27 2013 *)
Select[Table[FromDigits[PadLeft[{7}, n, 9]], {n, 25}], PrimeQ] (* Harvey P. Dale, Dec 12 2020 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Rick L. Shepherd, Mar 26 2004
EXTENSIONS
Name shortened and old name moved to comments by Alex Ratushnyak, Apr 26 2012
STATUS
approved