Numbers n such that 9*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103098
Numbers n such that 9*10^n + 4*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =30a(1) =41a(2) =228a(3) =581a(4) =1290a(5) =2580a(6) =3696a(7) =11390a(8) =21558
External references
- oeis: A103098