2016 Fermat Problem 4

An *oblong number* is the number of dots in a rectangular grid with one more row than column. The first four oblong numbers are 2, 6, 12, and 20, and are represented below:

What is the 7th oblong number?

\textbf{(A)}\ 42\quad \textbf{(B)}\ 49\quad \textbf{(C)}\ 56\quad \textbf{(D)}\ 64\quad \textbf{(E)}\ 72

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Fermat contests here.