A short proof of Cayley's tree formula

Abstract

We give a short proof of Cayley's tree formula for counting the number of different labeled trees on $n$ vertices. The following nonlinear recursive relation for the number of labeled trees on $n$ vertices is deduced from a combinatorial argument, $$ T_n = \frac{n}{2} \sum_{k=0}^{n-2} \left ( \begin {array} {c} n-2 \\ k \end {array} \right ) T_{k+1} T_{n-k-1}; \ \ for \ n > 1 \ and \ T_1 = 1, $$ and then it is proved that $T_n = n^{n-2}$, which gives yet another proof of the celebrated Cayley's tree formula.