Abstract
Our objects are (2.1) to introduce the graphical concept of a circular caterpillar together with cyclical code of non-negative integers, and (2.2) to provide an elementary example of the simplest kind of application of the celebrated Polya Enumeration Theorem.
Highlights
In general we follow the notation and terminology of [1,4]
The characterization if that T 2 is hamiltonian if and only if T does not contain SK1,3, the subdivision graph of the star Kt,3 as a subtree. This criterion says that T is a caterpillar, a tree whose "pruned subtree" T' is a path, called its spine, P5
The end-degree ed( u) of a node u of tree T is the number of nodes of degree 1 adjacent to u
Summary
In general we follow the notation and terminology of [1,4]. The wellknown species of trees called caterpillars were first discovered [9] when 1 asked my doctoral student, Allen Schwenk, wich trees T have a Hamiltonian square. This criterion says that T is a caterpillar, a tree whose "pruned subtree" T' (obtained by deleting all the endnodes of T) is a path, called its spine, P5 We [10] derived a formula for the number of caterpillars with n nodes having given spine P5
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