Numbers k such that 7*R_(k+2) - 3*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A257030
Numbers k such that 7*R_(k+2) - 3*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =5a(2) =23a(3) =182a(4) =209a(5) =287a(6) =7454a(7) =16958
External references
- oeis: A257030