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> Show that $1! +2! +3!+\cdots+n!$ is a perfect power if and only if $n =3$
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For $n=3$, $1!+2!+3!=9=3^2$. I also feel that the word 'power' makes it a whole lot hard to prove. How do we prove this? What technique do we use? 

I don't have any idea how to proceed with this. I would love some hints.