Numbers k such that 7*R_k + 20 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A256426
Numbers k such that 7*R_k + 20 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =3a(2) =5a(3) =17a(4) =44a(5) =47a(6) =78a(7) =504a(8) =533a(9) =768a(10) =915a(11) =1155a(12) =1313a(13) =7128a(14) =8088a(15) =15717a(16) =33074a(17) =43568a(18) =58689a(19) =82517a(20) =85647a(21) =154211
External references
- oeis: A256426