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%I #20 Jan 22 2023 17:09:52
%S 2,29,2999,2999999,29999999,29999999999999999999,
%T 2999999999999999999999999999,
%U 29999999999999999999999999999999999999999999,29999999999999999999999999999999999999999999999999999999
%N Primes of the form 2999...999.
%C a(9)=29999999999999999999999999999999999999999999999999999999. - _Vincenzo Librandi_, Aug 07 2010
%C The next term (a(10)) has 208 digits, and a(11) has 1312 digits. - _Harvey P. Dale_, Jan 22 2023
%e 3*10^k - 1 is prime for {1,3,6,7,19,27,43,55,207}; k gives the number of 9's in these numbers.
%t Select[Table[FromDigits[PadRight[{2}, n, 9]], {n, 60}], PrimeQ] (* _Harvey P. Dale_, Jan 22 2023 *)
%Y Cf. A051200.
%K base,nonn
%O 1,1
%A _Labos Elemer_, Jul 10 2000
%E Erroneous Formula entry removed by _Jon E. Schoenfield_, Jan 14 2018
%E Extended by _Harvey P. Dale_, Jan 22 2023
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