Thanks for your response, Frank! However, this unfortunately doesn't work for me, because the syntax error is preventing any output from being returned in order to show me the full form. It only shows me the full form if I use it on the correct expression.
There seems to be some problem in the keystrokes I am using to attempt to reproduce the form of the summation, whereas you were able to enter it correctly. What did you do to make the "n" variables show up correctly in gray while the s is in blue? I'm still new so I am not sure of the significance of these colors or how to get mathematica to interpret my variables correctly.
What I did was I entered the sum symbol, then used keyboard shortcuts to enter the infinity overscript and n=1 underscript, and then entered the expression with n and s next to the sum symbol. What am I missing with these "n"s? It's just a regular "n" on a keyboard right?
Edit: I am attaching a notebook with my expression as the last line.