\documentclass{article}
\usepackage{ifxetex}
\ifxetex
\usepackage{fontspec}
\else
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
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\title{Title of Document}
\author{Name of Author}
\usepackage{sagetex}
\begin{document}
\maketitle
It's $\sage{factor(2020)}$.
\end{document}