1,1

a(n)=2*10^n-1 and is prime

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

A051200.

Sequence in context: A067272 A037071 A065582 this_sequence A160452 A113596 A155670

Adjacent sequences: A055555 A055556 A055557 this_sequence A055559 A055560 A055561

base,nonn

Labos E. (labos(AT)ana.sote.hu), Jul 10 2000