Numbers k such that 10^k + 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A102931
Numbers k such that 10^k + 2*R_k + 7 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =3a(2) =6a(3) =51a(4) =57a(5) =63a(6) =150a(7) =393a(8) =420a(9) =547a(10) =42024a(11) =43063a(12) =101613a(13) =107385
External references
- oeis: A102931