Factorial Calculator
Calculate factorial (n!) and double factorial (n!!). Useful for permutations, combinations, and mathematical calculations.
Inputs
Results
Factorial (n!)
120
Double Factorial (n!!)15
How to Use This Calculator
- Enter a non-negative integer n in the Number field; n! is defined as 1 × 2 × 3 × … × n, with 0! = 1.
- Factorial grows extremely fast — n = 20 gives 2.4 × 10¹⁸, so very large inputs return scientific notation.
- Double Factorial (n!!) multiplies only every other integer: for odd n, n!! = n × (n−2) × … × 3 × 1.
- Factorials are the foundation of permutations (P(n,r) = n!/(n−r)!) and combinations (C(n,r) = n!/(r!(n−r)!)).
- Non-negative integers only — negative inputs and decimals are not supported by standard factorial.
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Formula
n! = n × (n-1) × (n-2) × ... × 2 × 1Related Calculators
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