Let $G = ( S , A )$ be a graph with $| S | = n \geq 2$. We write $\chi _ { G } ( X ) = X ^ { n } + \sum _ { k = 0 } ^ { n - 1 } a _ { k } X ^ { k }$. Give the value of $a _ { n - 1 }$ and express $a _ { n - 2 }$ in terms of $| A |$.
Let $G = ( S , A )$ be a graph with $| S | = n \geq 2$. We write $\chi _ { G } ( X ) = X ^ { n } + \sum _ { k = 0 } ^ { n - 1 } a _ { k } X ^ { k }$.\\
Give the value of $a _ { n - 1 }$ and express $a _ { n - 2 }$ in terms of $| A |$.