4! = 24
The perfect square factors of 4! are 1 and 4.
5! = 120
The perfect square factors of 5! are 1 and 4.
6! = 720
The perfect square factors of 6! are 1, 4, 9, 16, 36, and 144.
Those are the perfect square factors of the big product as well:
1, 4, 9, 16, 36, and 144 .
