Numbers n such that 4*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A102996
Numbers n such that 4*10^n + 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =2a(1) =4a(2) =26a(3) =1271a(4) =1412a(5) =3328a(6) =4676a(7) =47051a(8) =67664
External references
- oeis: A102996