On odd covering systems with distinct moduli

A famous unsolved conjecture of P. Erdos and J.L. Selfridge states that there does not exist a covering system {a"s(modn"s)}"s"="1^k with the moduli n"1,...,n"k odd, distinct and greater than one. In this paper we show that if such a covering system {a"s(modn"s)}"s"="1^k exists with n"1,...,n"k all square-free, then the least common multiple of n"1,...,n"k has at least 22 prime divisors.