Stein’s method and Narayana numbers

Abstract

Narayana numbers appear in many places in combinatorics and probability, and it is known that they are asymptotically normal. Using Stein’s method of exchangeable pairs, we provide an error of approximation in total variation to a symmetric binomial distribution of order n−1, which also implies a Kolmogorov bound of order n−1∕2 for the normal approximation. Our exchangeable pair is based on a birth–death chain and has remarkable properties, which allow us to perform some otherwise tricky moment computations. Although our main interest is in Narayana numbers, we show that our main abstract result can also give improved convergence rates for the Poisson-binomial and the hypergeometric distributions.