Numbers k such that 5*R_k + 10^k - 4 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
A259122
Numbers k such that 5*R_k + 10^k - 4 is prime, where R_k = 11...11 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =2a(2) =4a(3) =20a(4) =32a(5) =400a(6) =562a(7) =7016a(8) =37684
External references
- oeis: A259122