A binary tree is full if all of its vertices have either zero or two children. Let Bn denote the number of full binary trees with n vertices.

(a) By drawing out all full binary trees with 3, 5, or 7 vertices, determine the exact values of B3, B5, and B7. Why have we left out even numbers of vertices, like B4?
(b) For general n, derive a recurrence relation for Bn.
(c) Show by induction that Bn is (2n).