A binary tree is $f u l l$ if all of its vertices have either zero or two children. Let $B_{n}$ 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 $B_{3}, B_{5},$ and $B_{7},$ Why have we left out even numbers of vertices, like $B_{4} ?$
(b) For general $n,$ derive a recurrence relation for $B_{n^{*}}$
(c) Show by induction that $B_{n}$ is $\Omega\left(2^{n}\right)$.