Numbers k such that 2*10^k + 5*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A098930
Numbers k such that 2*10^k + 5*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =3a(2) =5a(3) =6a(4) =12a(5) =186a(6) =435a(7) =1746a(8) =3447a(9) =18798a(10) =70209
External references
- oeis: A098930