As Урош and Bernard said in the comments, it's quite probable that the original was set in Utopia and that therefor you could use fourier-otf (which actually is Erewhon, which is based on Heuristica which in turn, is based on Utopia) with XeLaTeX:
\documentclass[a5paper]{article}
\usepackage{fourier-otf}
\usepackage{amsmath}
\usepackage{unicode-math}
\usepackage{parskip}
\begin{document}
\textbf{Example 1}\
Let ((s_n)) be the sequence defined by (s_n = n^2(-1)^n). The
positive terms of this sequence comprise a subsequence. In this case,
the sequence ((s_n)) is
[(-1, 4, -9, 16, -25, 36, -49, 64,...)]
and the subsequence is
[(4, 16, 36, 64, 100, 144,...).]
More precisely, the subsequence is ((s_{n_k}){k\in\mathbb{N}}) where
(n_k =2k) so that (s{n_k} =(2k)^2 (-1)^{2k}=4k^2). The selection
function (\sigma) is given by (\sigma(k)=2k).
\end{document}

heuristica. – Урош Nov 18 '20 at 15:36Adobe Utopia, you might take a look atfourier, or evenfourier-otfif you want to use open-type fonts. – Bernard Nov 18 '20 at 15:47