Permutations and combinations – The factorial function

📘 Notes

The Factorial Function

Factorials are used to count arrangements and selections in probability and combinatorics.

For any positive integer \(n\):

\[ n! = n(n-1)(n-2)\dots 3\times2\times1 \]

Special case:

\[ 0! = 1 \]

\[ 5! = 5\times4\times3\times2\times1 = 120 \] \[ 4! = 24 \] \[ 3! = 6 \]