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

A102958

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

Terms

    a(0) =0a(1) =1a(2) =4a(3) =10a(4) =165a(5) =228a(6) =384a(7) =2890a(8) =3445a(9) =10069a(10) =17356a(11) =25804a(12) =29052a(13) =29082

External references