Factorial Calculator
Calculate n!, permutations & combinations
How to Use
1
Choose calculation
Select Factorial (n!), Permutation P(n,r), or Combination C(n,r).
2
Enter values
Input n (and r for permutations/combinations).
3
View result
See the exact result and formula used in the calculation.
Frequently Asked Questions
What is a factorial?
n! = n × (n-1) × (n-2) × ... × 1. Example: 5! = 5×4×3×2×1 = 120. By definition, 0! = 1.
What are permutations used for?
Permutations count arrangements where order matters. P(n,r) = n!/(n-r)! counts r items from n choices.
What are combinations used for?
Combinations count selections where order doesn't matter. C(n,r) = n!/[r!(n-r)!] counts r items from n.
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