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Possible Duplicate:
How to prove that the number 1!+2!+3!+…+n! is never square?

Show that $\displaystyle\sum\limits_{i=1}^k i!$ is never a perfect square for $k\ge4$

I could prove $k!$ is never a perfect square using Bertrand's Postulate. But this one seems to be an uphill task.

4 Answers 4