Exercise 5.
Use polynomial fitting to find a closed formula for the sequence \((a_n)_{n\ge 1}\text{:}\)
\begin{equation*}
4, 11, 20, 31, 44, \ldots
\text{.}
\end{equation*}
Use polynomial fitting to find a closed formula for the sequence \((a_n)_{n\ge 1}\text{:}\)