Consider the product 1! x 2! x 3! x … x 99! x 100! — a very big number, but that doesn’t faze us mathematicians (since you won’t need to multiply out in any event).
The puzzle: Can you, by omitting exactly one of the factorials from the product, produce a perfect square? (For instance, omitting 3! would make the product be 1! x 2! x 4! x 5! x … x 99! x 100!.)