Numbers k such that 7*R_k - 4 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A099420
Numbers k such that 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) =3a(3) =5a(4) =9a(5) =12a(6) =15a(7) =21a(8) =264a(9) =383a(10) =2720a(11) =4494a(12) =21167a(13) =45825a(14) =55851a(15) =64568a(16) =70727
External references
- oeis: A099420