For each positive integer $n$, the expression $1+2+3+\cdots+(n-1)+n$ represents the sum of all of the integers from 1 to $n$ inclusive. What integer is equal to

$$
(1+2+3+\cdots+2020+2021)-(1+2+3+\cdots+2018+2019) ?
$$
By regrouping terms, we have

$$
\begin{aligned}
& (1+2+3+\cdots+2020+2021)-(1+2+3+\cdots+2018+2019) \\
= & (1+2+3+\cdots+2018+2019)+2020+2021-(1+2+3+\cdots+2018+2019) \\
= & 2020+2021 \\
= & 4041 .
\end{aligned}
$$

ANSWER: 4041