Numbers k such that 7*R_(k+2) - 10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A257032
Numbers k such that 7*R_(k+2) - 10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =3a(1) =9a(2) =132a(3) =8547a(4) =13215a(5) =14110
External references
- oeis: A257032