OFFSET
1,2
COMMENTS
Also numbers k such that (7*10^(k+1)+11)/9 is prime.
a(12) > 2*10^5. - Tyler Busby, Feb 01 2023
LINKS
FORMULA
a(n) = A098089(n+1) - 1. - Robert Price, Nov 22 2014
MATHEMATICA
Do[ If[ PrimeQ[70*(10^n - 1)/9 + 9], Print[n]], {n, 0, 5000}]
Select[Range[700], PrimeQ[(7 10^(# + 1) + 11) / 9] &] (* Vincenzo Librandi, Nov 22 2014 *)
PROG
(Magma) [n: n in [1..400] | IsPrime((7*10^(n+1)+11) div 9)]; Vincenzo Librandi, Nov 22 2014
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
EXTENSIONS
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(9) derived from A098089 by Robert Price, Nov 22 2014
a(10)-a(11) from Tyler Busby, Feb 01 2023
STATUS
approved