So in Jekyll and Markdown, I can't type $ or its HTML equivalent code, and not \$ nor $\$$. How should I type the dollar sign?
The dollar sign "$" has Unicode code point U+0024 (inherited from ASCII via Latin-1).
dollar sign: \$ Curly brace: \{ or \} Ampersand: \&
In markdown editors such as GitHub , or Jupyter notebook , with MathJax available, you can use double backslash and a dollar sign together to show any amount or range of amount in the dollar. Note that, in StackExchange or any StackOverflow related site, a single backslash is enough.
Enable processEscapes:
MathJax.Hub.Config({
  tex2jax: {
    inlineMath: [['$','$'], ['\\(','\\)']],
    processEscapes: true
  }
});
Then you can simply use \$ to get a plain $.
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