Find $\displaystyle \sum_{n = 1}^4 (2k + 1)$.

$\begin{align} \displaystyle \sum_{k = 1}^4 (2 \cdot k + 1) & = (2 \cdot 1 + 1) + (2 \cdot 2 + 1) + (2 \cdot 3 + 1) + (2\cdot 4 + 1) \\ & = 3 + 5 + 7 + 9 \\ \\ & = 24 \end{align}$
 

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