I'm no coder but....I think it's because you put: Zeta[s] instead of: s = Zeta[n]...I might be wrong, but it seems like that to me.

Here is a screenshot of each expression in a new, clean notebook. I am trying to figure out why the sum I type will not evaluate, but the sum I copy-paste from a tutorial does evaluate to the correct Zeta[s] output.

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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.

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What happens if you enter the expression as

In[2]:= Sum[n^-s, {n, 1, \[Infinity]}]

Out[2]= Zeta[s]

?

Ahh! As I said, I am extremely new to this and am just beginning with the built-in tutorials; I didn't actually know about the palette yet. I thought I had to enter fancy expressions using only keyboard shortcuts, silly me. When I use the palette it works fine, since it has explicitly delineated fields for the index and expression. I just couldn't figure out how to impart this information using only shortcuts but now I know I don't have to.

Thank you all very much!