Numbers k such that 7*10^k + 6*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

A103063

Numbers k such that 7*10^k + 6*R_k - 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Terms

    a(0) =0a(1) =1a(2) =2a(3) =6a(4) =25a(5) =69a(6) =253a(7) =300a(8) =384a(9) =434a(10) =721a(11) =822a(12) =883a(13) =2192a(14) =2649a(15) =3441a(16) =3445a(17) =8028a(18) =11655

External references