Numbers n such that 2*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A102956
Numbers n such that 2*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =1a(1) =82a(2) =322a(3) =733a(4) =2431a(5) =8386a(6) =15886a(7) =19912
External references
- oeis: A102956