Numbers n such that 9*10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
A103106
Numbers n such that 9*10^n + 7*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
Terms
- a(0) =0a(1) =6a(2) =15a(3) =36a(4) =45a(5) =447a(6) =1031a(7) =1239a(8) =3492a(9) =6069a(10) =13647a(11) =17238a(12) =56271a(13) =72711a(14) =75381
External references
- oeis: A103106