Numbers k such that 5*10^k + 4*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A103014
Numbers k such that 5*10^k + 4*R_k - 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =3a(2) =4a(3) =9a(4) =12a(5) =60a(6) =268a(7) =289a(8) =384a(9) =795a(10) =3474a(11) =9180a(12) =76438
External references
- oeis: A103014