The Proportion of Permutations Fixing a k-Set
An asymptotic formula for $p(k)$, the limiting probability that a random permutation has an invariant set of size $k$: it is asymptotically $k^{-\delta}(1+o(1))$ times a smooth positive function, sharpening a line of estimates running through Łuczak-Pyber and Eberhard-Ford-Green.