Squares + Triangles!

In figure 1, there are $12$ quadrilaterals.
In figure 2, there are $28$ quadrilaterals.
In figure 3, there are $48$ quadrilaterals.
(For more clarification):-
In figure 4, there are $72$ quadrilaterals.
In figure 5, there are $100$ quadrilaterals.

So, we observe that in the $n^{\text{th}}$ figure, the number of quadrilaterals is found by the formula:-
$12n + (4 × \displaystyle \sum_{n=1}^{n} (n - 1))$

$\therefore$ In the $2016^{\text{th}}$ figure that follows this pattern, there would be:-
$(12 × 2016) + (4 × \displaystyle \sum_{n=1}^{2016} (n - 1))$
$= (12 × 2016) + (4 × \dfrac{2015 × 2016}{2})$
$= (12 × 2016) + (2016 × 4030)$
$= (2016 × 4042)$
= 8148672 quadrilaterals. $_\square$