Numbers k such that 20*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A056678
Numbers k such that 20*R_k + 9 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =1a(1) =2a(2) =4a(3) =13a(4) =175a(5) =415a(6) =2504a(7) =2758a(8) =7924a(9) =9400a(10) =10390a(11) =12104a(12) =19615
External references
- oeis: A056678