Numbers k such that 10^k + 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A102942
Numbers k such that 10^k + 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =2a(2) =8a(3) =26a(4) =44a(5) =167a(6) =185a(7) =3818a(8) =8741a(9) =50795
External references
- oeis: A102942