This is a post written in plain Markdown (*.md) instead of R Markdown (*.Rmd). The major differences are:

1. You cannot run any R code in a plain Markdown document, whereas in an R Markdown document, you can embed R code chunks (```{r});
2. A plain Markdown post is rendered through Blackfriday, and an R Markdown document is compiled by rmarkdown and Pandoc.

There are many differences in syntax between Blackfriday’s Markdown and Pandoc’s Markdown. For example, you can write a task list with Blackfriday but not with Pandoc:

• Write an R package.
• Write a book.
• …
• Profit!

Similarly, Blackfriday does not support LaTeX math and Pandoc does. I have added the MathJax support to this theme (hugo-lithium) but there is a caveat for plain Markdown posts: you have to include math expressions in a pair of backticks (inline: `$ $`; display style: `$$ $$`), e.g., $S_n = \sum_{i=1}^n X_i$.¹ For R Markdown posts, you do not need the backticks, because Pandoc can identify and process math expressions.

When creating a new post, you have to decide whether the post format is Markdown or R Markdown, and this can be done via the ext argument of the function blogdown::new_post(), e.g.

blogdown::new_post("Post Title", ext = '.Rmd')