Numbers n such that 8*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103083
Numbers n such that 8*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =21a(1) =27a(2) =60a(3) =471a(4) =1074a(5) =5781
External references
- oeis: A103083