Numbers k such that 2*R_k + 9*10^k + 7 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
A259140
Numbers k such that 2*R_k + 9*10^k + 7 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =6a(2) =12a(3) =110a(4) =3608a(5) =37784
External references
- oeis: A259140