begin{equation}
a^2 + b^2 = c^2
end{equation}

(@foo)  $a^2 + b^2 = c^2$

As (@foo) says, ...

(@bar)  $e = x + y$

a^2 + b^2 = c^2

<script type="text/x-mathjax-config">
  MathJax.Hub.Config({ TeX: { equationNumbers: {autoNumber: "all"} } });
</script>

pandoc math.txt -t html -s -o test.html --mathjax=https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML -H header