Numbers k such that 7*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A103057

Numbers k such that 7*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =1a(1) =4a(2) =6a(3) =7a(4) =10a(5) =16a(6) =22a(7) =31a(8) =1315a(9) =2064a(10) =6150a(11) =8707a(12) =12252a(13) =18610a(14) =21630a(15) =41712a(16) =44808a(17) =45421

External references