Numbers k such that 9*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A103097
Numbers k such that 9*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =4a(2) =8a(3) =2960a(4) =4571a(5) =5201a(6) =17864a(7) =21922a(8) =89375a(9) =147676
External references
- oeis: A103097