Long unsplittable zero-sum sequences over a finite cyclic group
Let [Formula: see text] be an additively written finite cyclic group of order [Formula: see text] and let [Formula: see text] be a minimal zero-sum sequence with elements of [Formula: see text], i.e. the sum of elements of [Formula: see text] is zero, but no proper nontrivial subsequence of [Formula: see text] has sum zero. [Formula: see text] is called unsplittable if there do not exist an element [Formula: see text] in [Formula: see text] and two elements [Formula: see text] in [Formula: see text] such that [Formula: see text] and the new sequence [Formula: see text] is still a minimal zero-sum sequence. In this paper, we investigate long unsplittable minimal zero-sum sequences over [Formula: see text]. Our main result characterizes the structures of all such sequences [Formula: see text] and shows that the index of [Formula: see text] is at most 2, provided that the length of [Formula: see text] is greater than or equal to [Formula: see text] where [Formula: see text] is a positive integer with least prime divisor greater than [Formula: see text].