How did you get it to work?
There’s a separate unicode character for ². It doesn’t require HTML tags. It’s like the @ character, or the ± character. It’s actually a distinct 16-bit character.
In Windows, you have a Character Map program. Just click your start button and type in “char” and it will pop up for you to click.
If you’re using Linux, I’m sure there’s an equivalent, but I don’t know how to get to it.