Numbers n such that 5*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103021
Numbers n such that 5*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =0a(1) =1a(2) =3a(3) =7a(4) =15a(5) =27a(6) =129a(7) =189a(8) =333a(9) =1324a(10) =1600a(11) =2199a(12) =10000a(13) =27751
External references
- oeis: A103021