A tripod is a tree having exactly three tree leaves (Pirnazar and Ullman 2002). The numbers of tripods on , 2, ... vertices are 0, 0, 0, 1, 1, 2, 3, 4, 5, 7, 8, 10,
12, 14, 16, ... (OEIS A001399), the first of
which are illustrated above.
A list of tripods on small numbers of vertices is implemented in the Wolfram
Language as GraphData["Tripod"].
Pirnazar, A. and Ullman, D. H. "Girth and Fractional Chromatic Number of Planar Graphs." J. Graph Th.39, 201-217,
2002.Sloane, N. J. A. Sequence A001399/M0518
in "The On-Line Encyclopedia of Integer Sequences."