hi i don't seem to have that symbol on my keyboard. trigger.
If you mean showing x_0 instead of x^n, use shift "-". If you are talking about subscripts and super scripts (there is no such thing as "lowercase" numbers) it is not any single key: enter [ math ] without the spaces, then enter the latex and, finally, [ \math ], again without the spaces.
For example .
Clicking on that expression should show you the code.