Metric properties of the Tower of Hanoi graphs and Stern’s diatomic sequence

AbstractIt is known that in the Tower of Hanoi graphs there are at most two different shortest paths between any fixed pair of vertices. A formula is given that counts, for a given vertex v, the number of vertices u such that there are two shortest u,v-paths. The formula is expressed in terms of Stern’s diatomic sequence b(n) (n≥0) and implies that only for vertices of degree two this number is zero. Plane embeddings of the Tower of Hanoi graphs are also presented that provide an explicit description of b(n) as the number of elements of the sets of vertices of the Tower of Hanoi graphs intersected by certain lines in the plane