Computing the Greatest Common Divisor of Binomial Coefficients $\binom{mn}{mk}$

Abstract

The greatest common divisor (GCD) of $\binom{2n}{2k}$ for $1\leq k<n$ is known to be some power of 2 times the product of all odd primes p such that $2n=p^i+p^j$. We complete the analysis of this GCD by showing that this power of 2 is either 1 or 0 and relates it to Mersenne primes. We also show how to efficiently compute GCD${\binom{mn}{mk}: 1\leq k<n}$ when n satisfies certain conditions.