Numbers k such that 2*10^k + 7*R_k - 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A098960
Numbers k such that 2*10^k + 7*R_k - 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =2a(1) =6a(2) =33a(3) =69a(4) =150a(5) =936a(6) =3135a(7) =5838a(8) =6990a(9) =20786a(10) =57138
External references
- oeis: A098960