Numbers k such that 9*R_(k+2) - 10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A257041
Numbers k such that 9*R_(k+2) - 10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =3a(1) =4a(2) =5a(3) =9a(4) =19a(5) =25a(6) =34a(7) =70a(8) =82a(9) =718a(10) =2035a(11) =2494a(12) =3369a(13) =3953a(14) =4219a(15) =8524a(16) =30943a(17) =49375a(18) =52082a(19) =139670a(20) =303255
External references
- oeis: A257041