Numbers k such that 5*10^k + 2*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A103008

Numbers k such that 5*10^k + 2*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =2a(1) =9a(2) =12a(3) =15a(4) =26a(5) =45a(6) =62a(7) =80a(8) =128a(9) =326a(10) =494a(11) =614a(12) =710a(13) =1641a(14) =1646a(15) =2103a(16) =8514a(17) =8688

External references