I had seen this post, and the way Lithium works I can not find that post.  So here is a suggestion.

For most purposes, you can use the  tag to create super script text and  to create sub-script text. See examples below:

Code: x<sup>x+1</sup>
Result: x^x+1

Code: x<sub>i+1</sub>
Result: x_i+1

Note: Although some Web standards professionals recommend avoiding these tags, they are an official XHTML standard.

I have no idea if you need a <p> tag or not.  On short sentences like:

This is a test^ttt it does work

The way to do it in weebly is to use embed code feature.  Open the embed code

Type in your text as

This is a test for superscript^x+1.....

Reference: http://symbolcodes.tlt.psu.edu/web/tips/superscript.html