An integer multiplied by which number leaves it unchanged?

Count the number of negative factors:
- **Even** number of negatives → product is positive.
- **Odd** number of negatives → product is negative.

Examples: $(-2)\times (-3)\times (-4)$ has three negatives (odd) → negative. Compute the magnitude: $2\times 3\times 4=24$. Result: −24.

$(-2)\times (-3)\times 4$ has two negatives (even) → positive. Magnitude: $2\times 3\times 4=24$. Result: +24.