Numbers k such that 20*R_k + 1 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.
A056660
Numbers k such that 20*R_k + 1 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =3a(1) =17a(2) =99a(3) =120a(4) =243a(5) =545a(6) =630a(7) =1493a(8) =2565a(9) =8087
External references
- oeis: A056660