Numbers n such that 4*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A102984
Numbers n such that 4*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =0a(1) =1a(2) =2a(3) =4a(4) =7a(5) =22a(6) =23a(7) =80a(8) =4427a(9) =31319a(10) =80150a(11) =91144
External references
- oeis: A102984