Factorials count arrangements: there are 5! = 120 ways to line up five people and 52! ≈ 8 × 10⁶⁷ ways to shuffle a deck of cards. They grow faster than any exponential function, which is why exact calculation needs big-integer arithmetic.
How to use the Factorial Calculator
- Number n
Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
The calculator multiplies with exact whole numbers (BigInt) in your browser. Trailing zeros come from factors of 10 = 2 × 5; there are ⌊n/5⌋ + ⌊n/25⌋ + … of them.
Formula
n! = n × (n − 1) × … × 2 × 1, 0! = 1
Worked example
Inputs — Number n: 25.
Results — n! = 15,511,210,043,330,985,984,000,000 (≈ 1.551121 × 10²⁵, 26 digits); Scientific notation = 1.551121004 × 10²⁵; Number of digits = 26; Trailing zeros = 6.
Key terms
- Factorial
- The product of all positive integers up to n.
Frequently asked questions
Why is 0! = 1?
There is exactly one way to arrange nothing, and it keeps formulas such as n! = n × (n − 1)! consistent.
What is 10!?
3,628,800.
Can factorials be defined for fractions?
Yes, through the gamma function: x! = Γ(x + 1).
How many trailing zeros does 100! have?
24.