Limit Theorems for Descents in Permutations and Arithmetic Progressions in mathbb{Z}/pmathbb{Z}

We prove a quantitative local limit theorem for the number of descents in a random permutation. Our proof uses a conditioning argument and is based on bounding the characteristic function $\phi(t)$ of the number of descents. We also establish a central limit theorem for the number of 3-term arithmetic progressions (3-APs) in a random subset of $\mathbb{Z}/p\mathbb{Z}$. We conjecture that there is no local limit theorem for 3-APs, but a proof of this remains elusive. A promising avenue of proof is to condition on the size of the subset and show that the resulting distributions are too far apart for different sizes. This has proven difficult because the distances between these conditioned distributions on are the same order as their standard deviations such that the constant multiple between them is not very large.