Doesn't work on numbers, you have to precede the number with an apostrophe or
format the cell as text first, and then you can select just that part of the
string and format as Superscript.
Just to clarify, when I say doesn't work on numbers, I mean you can't apply it
to just part of a number. You can always format the entire cell as superscript,
although that isn't what you want obviously.