Mathematics
What is Factorials?
A factorial, written with an exclamation mark (like 5!), means multiplying a whole number by every whole number below it down to 1. So 5! = 5 × 4 × 3 × 2 × 1 = 120. Factorials count how many ways things can be arranged.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains factorials.
Key things to understand
- 1n! means n × (n−1) × … × 1.
- 2For example, 4! = 4 × 3 × 2 × 1 = 24.
- 3By definition, 0! = 1.
- 4They count arrangements, key to permutations and probability.
Frequently asked questions
- What is a factorial?
- The product of a whole number and all smaller positive whole numbers, written like 5! = 120.
- What is 0 factorial?
- By definition, 0! equals 1 — there's exactly one way to arrange nothing.
- What are factorials used for?
- Counting arrangements and selections, which is central to permutations, combinations, and probability.