Counting of lattices containing up to five comparable reducible elements and having nullity up to three

Abstract

In 2020 Bhavale and Waphare introduced the concept of a nullity of a poset as nullity of its cover graph. In 2003 Pawar and Waphare counted all non-isomorphic lattices on n elements and n edges, which are precisely lattices of nullity one. In 2002 Thakare et al. counted all non-isomorphic lattices on n elements containing two reducible elements. In the same paper, Thakare et al. counted lattices on n elements containing up to n+1 edges, which are precisely lattices of nullity up to two. In 2024 Bhavale and Aware counted all non-isomorphic lattices on n elements, containing up to three reducible elements. Recently, Aware and Bhavale counted all non-isomorphic lattices on n elements, containing four comparable reducible elements, and having nullity three. In this paper, we count up to isomorphism the class of all lattices on n elements containing five comparable reducible elements, and having nullity three.