Numbers k such that 5*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A103013
Numbers k such that 5*10^k + 4*R_k - 3 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =2a(2) =3a(3) =86a(4) =134a(5) =185a(6) =344a(7) =396a(8) =476a(9) =834a(10) =1799a(11) =2147a(12) =2418a(13) =5216a(14) =5882a(15) =6216a(16) =13394a(17) =19746a(18) =66485
External references
- oeis: A103013