Numbers n such that 8*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103074
Numbers n such that 8*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =0a(1) =2a(2) =3a(3) =5a(4) =17a(5) =47a(6) =177a(7) =8462a(8) =36615
External references
- oeis: A103074