help solve it

What is the largest number that will always divide the sum of any 8 consecutive positive integers?

My attempt:

$\begin{array}{|rcll|} \hline \text{sum} &=& \dfrac{(a_1+a_8)}{2}\times 8 \\\\ \text{sum} &=& (a_1+a_8)\times \color{red}4 \\ \hline \end{array}$

The largest number is $\color{red} 4$