Numbers n such that 4*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A102993
Numbers n such that 4*10^n + 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =6a(1) =21a(2) =22a(3) =24a(4) =51a(5) =81a(6) =132a(7) =165a(8) =621a(9) =1450a(10) =3424a(11) =5979a(12) =11526a(13) =26980a(14) =49233a(15) =84927
External references
- oeis: A102993