Factorial Calculator
Calculate factorials, double factorials, and subfactorials with various options and formats.
Factorial Calculator
Enter a non-negative integer (max 170 for standard factorial)
Calculation Results
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Factorial Types
Standard (n!):
n! = n × (n-1) × (n-2) × ... × 2 × 1
Double (n!!):
n!! = n × (n-2) × (n-4) × ... × 2 or 1
Subfactorial (!n):
!n = n! × Σ(-1)^k / k! for k=0 to n
Multifactorial:
n!(k) = n × (n-k) × (n-2k) × ... × remainder
Factorial Tips
- 0! = 1 by definition
- Factorials grow very quickly
- Use for permutations and combinations
- Common in probability and statistics
Calculation History
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