Numbers k such that 40*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A056683
Numbers k such that 40*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =4a(2) =5a(3) =47a(4) =107a(5) =244a(6) =1043a(7) =20207a(8) =52739a(9) =89188
External references
- oeis: A056683