Factorial for small non-negative integers up to 20 (fits normal floating display).
It multiplies 2×3×…×n (and defines 0! = 1 via an empty product loop). Larger factorials exceed safe JavaScript integer precision—only 0–20 is accepted.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.