Numbers n such that 4*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A102995
Numbers n such that 4*10^n + 7*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =1a(1) =22a(2) =925a(3) =2340a(4) =15955a(5) =16098a(6) =55512a(7) =82752
External references
- oeis: A102995