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

A103010

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

Terms

    a(0) =3a(1) =5a(2) =33a(3) =48a(4) =59a(5) =60a(6) =74a(7) =126a(8) =177a(9) =228a(10) =638a(11) =1304a(12) =1644a(13) =2435a(14) =4374a(15) =8750a(16) =15114a(17) =16853a(18) =30353a(19) =30545a(20) =36236

External references