Numbers k such that 7*R_(k+2) - 6*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A257027
Numbers k such that 7*R_(k+2) - 6*10^k is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =2a(2) =3a(3) =9a(4) =11a(5) =18a(6) =74a(7) =131a(8) =144a(9) =161a(10) =224a(11) =282a(12) =390a(13) =398a(14) =614a(15) =791a(16) =1313a(17) =1866a(18) =9708a(19) =10544a(20) =13292a(21) =13394a(22) =29703a(23) =30779a(24) =72446
External references
- oeis: A257027