A operation that finds the product of a number followed by all natural numbers smaller than it. Notation n!=n(n−1)(n−2)…(1) You can only have integer factorial numbers n >= 0 Factorial of 0 0!=1 Because there is only 1 arrangement for 0 objects Concepts Factorial Division Factorial Factoring Factorial Base Changing Factorial Simplification Reverse Factorials Stirlings Approximation