How to Calculate Factorial Calculator n!
What is Factorial Calculator n!?
Factorial of n (written n!) is the product of all positive integers from 1 to n: n! = n × (n−1) × ... × 2 × 1. Factorials appear in combinations, permutations, probability, and Taylor series expansions.
Step-by-Step Guide
- 10! = 1 (by definition)
- 21! = 1, 2! = 2, 3! = 6, 4! = 24, 5! = 120
- 3n! = n × (n-1)!
- 4C(n,k) = n! / (k! × (n-k)!) — factorials underlie combination formulas
Worked Examples
Input
5!
Result
120
5×4×3×2×1 = 120
Input
10!
Result
3,628,800
About 3.6 million
Input
20!
Result
2.43 × 10¹⁸
Over 2 quintillion
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