11. Observe the following equations:
$$
\begin{array}{l}
1+3=4=2 \times 2 \\
1+3+5=9=3 \times 3 \\
1+3+5+7=16=4 \times 4 .
\end{array}
$$

Calculate: $1+3+5+\cdots \cdots+2019=$ $\qquad$
Reference answer: 1020100