Numbers k such that 8*10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A056724

Numbers k such that 8*10^k + 7*R_k is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =2a(1) =9a(2) =15a(3) =32a(4) =38a(5) =65a(6) =123a(7) =173a(8) =257a(9) =320a(10) =326a(11) =639a(12) =719a(13) =774a(14) =902a(15) =15210a(16) =69999

External references