There is of course the silly implementation:
FareySequence[n_] := Union[Flatten[Table[j/i, {i, 1, n}, {j, 0, i}]]]
However, there is this propertyare numerous properties and confinements of Farey sequences:
$$F_0=0, \ F_n=1, \\ F_k=F_{k-1} + 1/(D_kD_{k-1})$$
where $F$ is the Farey sequence and $D$ is the denominator sequence of(that can be used, $F$potentially, in reduced forman indirect manner).
This calls for a very simple, and, very efficient recurring/functional implementation, exhibiting Superiority. But I'm new to Mathematica and can't find the right combination of built-in functions, and pure functions..
Ideas?