Numbers k such that 7*R_(k+2) - 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A257029

Numbers k such that 7*R_(k+2) - 4*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =0a(1) =66a(2) =84a(3) =3366a(4) =14934

External references