Numbers k such that 20*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A056677
Numbers k such that 20*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =2a(2) =8a(3) =14a(4) =27a(5) =63a(6) =1167a(7) =1694a(8) =2361a(9) =116619
External references
- oeis: A056677