The factorial of a positive integer \(n\), is the product of all positive integers less than or equal to \(n\). The factorial of \(n\) is written as \(n!\).
By definition
\(2!=2\times1\)
\(3!=3\times2\times1\)
\(4!=4\times3\times2\times1\)
Therefore
\(n!=n\times(n-1)\times(n-2)\times(n-4)...\times2\times1\)
This can rewritten as
\(n!=n\times(n-1)!\)
