Unlabeled Topology

A rooted binary tree has an unlabeled shape that describes its branching structure. For trees with \(n\) leaves, \(n\geq1\), the number of distinct unlabeled shapes follows the sequence \(1, 1, 1, 2, 3, 6, 11, 23, 46, 98, …\), the Wedderburn-Etherington numbers; each tree with  \(n\) leaves has one of the possible unlabeled tree shapes, also termed unlabeled topologies.