Factorial Calculator
Calculate factorials, double factorials, and subfactorials
5! (Factorial)
120
Number of Digits
3
Trailing Zeros
1
Expression
5! = 5 × 4 × 3 × 2 × 1
Step by Step
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
All Factorial Types
Factorial (5!)
120
Double Factorial (5!!)
15
Subfactorial (!5)
44
Definitions
Factorial (n!)
n! = n × (n-1) × (n-2) × ... × 2 × 1
0! = 1 by definition
Double Factorial (n!!)
Product of integers from 1 to n with same parity
5!! = 5 × 3 × 1 = 15
Subfactorial (!n)
Number of derangements (permutations with no fixed points)
!n = (n-1)(!(n-1) + !(n-2))