On the index of length four minimal zero-sum sequences
Let G be a finite cyclic group. Every sequence S over G can be written in the form where g ∈ G and , and the index ind(S) is defined to be the minimum of over all possible g ∈ G such that ⟨g⟩ = G. A conjecture says that every minimal zero-sum sequence of length 4 over a finite cyclic group G with gcd(|G|,6) = 1 has index 1. This conjecture was confirmed recently for the case when |G| is a product of at most two prime powers. However, the general case is still open. In this paper, we make some...