superscripts in algebra 1

How can I enter a superscript of more than one character, such as n-1? When I keep typing the program bounces me back to the main line. When I click the superscript button for a second time it makes a superscript of the superscript. Also, how do I find a response to my question? I left it before and couldn't find any answer. Can't finish Sequences without being able to do this.

gretchenkromer@comcast.net