Numbers k such that 8*R_k + 7*10^k - 1 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
A259137
Numbers k such that 8*R_k + 7*10^k - 1 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =4a(2) =86a(3) =112a(4) =170a(5) =566a(6) =1688a(7) =8902a(8) =115810
External references
- oeis: A259137