Đáp án: $0$
Giải thích các bước giải:
Nếu $n$ chẵn $\to n+2020^{1919}$ chẵn
$\to (n+2020^{1919})\quad\vdots\quad 2$
$\to 5(n+2020^{1919})\quad\vdots\quad 2\cdot 5$
$\to 5(n+2020^{1919})\quad\vdots\quad 10$
$\to 5(n+2020^{1919})(n+2019^{1920})\quad\vdots\quad 10$
$\to 5(n+2020^{1919})(n+2019^{1920})$ tận cùng là $0$
Nếu $n$ lẻ $\to n+2019^{1920}$ chẵn
$\to (n+2019^{1920})\quad\vdots\quad 2$
$\to 5(n+2019^{1920})\quad\vdots\quad 2\cdot 5$
$\to 5(n+2010^{1920})\quad\vdots\quad 10$
$\to 5(n+2020^{1919})(n+2019^{1920})\quad\vdots\quad 10$
$\to 5(n+2020^{1919})(n+2019^{1920})$ tận cùng là $0$
