The concept of the brush number $b_r(G)$ was introduced for a simple connected undirected graph $G$. The concept will be applied to the Mycielskian graph $\mu(G)$ of a simple connected graph $G$ to find $b_r(\mu(G))$ in terms of an \emph{ optimal orientation} of $G$. We prove a surprisingly simple general result for simple connected graphs on $n \geq 2$ vertices namely: $b_r(\mu(G))= b_r(\mu^{ \rightarrow}(G)) = 2\sum\limits_{ i=1}^{ n}d^+_{ G^{ \rightarrow}_{ b_r(G)}}(v_i).$
Categories: math.CO