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

A102987

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

Terms

    a(0) =0a(1) =3a(2) =2043a(3) =5967a(4) =39855

External references