Numbers k such that 7*R_k - 20 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A256830
Numbers k such that 7*R_k - 20 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =3a(1) =4a(2) =24a(3) =106a(4) =124a(5) =162a(6) =243a(7) =258a(8) =1344a(9) =1386a(10) =2494a(11) =4200a(12) =5859a(13) =8844a(14) =13122a(15) =19908a(16) =86844a(17) =106066a(18) =180732
External references
- oeis: A256830