%I A055558
%S A055558 19,199,1999,199999,19999999,199999999999999999999999999,
%T A055558 1999999999999999999999999999,
%U A055558 199999999999999999999999999999999999999999999999999999
%N A055558 Primes of form 1999...999.
%F A055558 a(n)=2*10^n-1 and is prime
%e A055558 2*10^n-1 is prime for {1,2,3,5,7,26,27,53,147,236,248,386,401} n gives 
               how many digit 9 occurs in these numbers
%Y A055558 A051200.
%Y A055558 Sequence in context: A067272 A037071 A065582 this_sequence A160452 A113596 
               A155670
%Y A055558 Adjacent sequences: A055555 A055556 A055557 this_sequence A055559 A055560 
               A055561
%K A055558 base,nonn
%O A055558 1,1
%A A055558 Labos E. (labos(AT)ana.sote.hu), Jul 10 2000