Compute n! for any integer (powered by BigInt)
n! (n factorial) is the product of all positive integers less than or equal to n.
For example: 5! = 5 × 4 × 3 × 2 × 1 = 120
5! = 5 × 4 × 3 × 2 × 1 = 120
Special case: 0! = 1
0! = 1