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Factorial (n!)
n! is n × (n−1) × (n−2) × … × 1. The number of ways to line up n different things.
Factorial — n!
Multiply n by every smaller positive whole number.
5! = 120
n5
5×4×3×2×1=120
Why does it grow so fast?
- 5! = 120
- 10! = 3,628,800
- 15! ≈ 1.3 trillion
Why we set 0! = 1
There's exactly one way to line up zero things — the empty line-up. So 0! = 1, by convention, and everything else stays consistent.