Numbers k such that 7*R_k - 40 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A256828
Numbers k such that 7*R_k - 40 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =6a(2) =18a(3) =48a(4) =204a(5) =10386a(6) =19524a(7) =28320
External references
- oeis: A256828