What is the units digit of $\sum\limits_{n=1}^{1337}(n!)^4$ ? I find 9 but I am not sure.
2026-04-03 21:27:06.1775251626
What is the units digit of $\sum\limits_{n=1}^{1337} (n!)^4$?
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2
Hint
In mod $10$ we have $n!=0$ for $n\ge5$.