If you're writing about centuries, or ordinal numbers such as first, second, third, ... you might want to consider writing the following new commands and put them in your Latex document's preamble.
\newcommand{\superscript}[1]{\ensuremath{^\textrm{#1} }}
\newcommand{\subscript}[1]{\ensuremath{_\textrm{#1} }}
so you can write
Welcome to the 21\superscript{st} century.
other such quick commands can be written with
\newcommand{\th}[0]{\superscript{th}}
\newcommand{\st}[0]{\superscript{st}}
\newcommand{\nd}[0]{\superscript{nd}}
\newcommand{\rd}[0]{\superscript{rd}}
so you can write
Carl took 1\st place. Elly, Tom and Ann came in 2\nd, 3\rd and 4\th.
Stephan Bode wrote in to tell about the
\textsuperscript that allows to put superscript in text, without having to resort to our own commands. Unfortunately, there is no such thing as a
\textsubscript in
LaTeX's defaults ...