Numbers n such that 5*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103022
Numbers n such that 5*10^n + 8*R_n - 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =3a(1) =5a(2) =6a(3) =21a(4) =309a(5) =816a(6) =858a(7) =1115a(8) =1419a(9) =1689a(10) =12009a(11) =18693a(12) =28098a(13) =90965
External references
- oeis: A103022