Numbers k such that 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A099409
Numbers k such that 2*R_k + 5 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =1a(2) =3a(3) =9a(4) =15a(5) =28a(6) =64a(7) =1168a(8) =1695a(9) =2362a(10) =116620a(11) =336405
External references
- oeis: A099409