Numbers k such that R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
A097683
Numbers k such that R_k + 2 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
Terms
- a(0) =0a(1) =1a(2) =2a(3) =3a(4) =5a(5) =9a(6) =11a(7) =24a(8) =84a(9) =221a(10) =1314a(11) =2952a(12) =20016a(13) =51054
External references
- oeis: A097683