Numbers n such that 5*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103023
Numbers n such that 5*10^n + 8*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =2a(1) =6a(2) =8a(3) =20a(4) =108a(5) =288a(6) =306a(7) =462a(8) =20102a(9) =30042a(10) =69050
External references
- oeis: A103023