When is 1+2+ +n a perfect square?

[CornMuffin]

Homework Statement

Find the values of $$n\geq 1$$ for which 1! + 2! + ... + n! is a perfect square in the integers.

Homework Equations

The Attempt at a Solution

n=1 and n=3 works, but I don't know how to find anymore, or prove that there aren't anymore

 

[Petek]

Do you know about quadratic residues? If so, that's a hint.

 

[CornMuffin]

Do you know about quadratic residues? If so, that's a hint.

well I proved it, thanks