Falling factorial
From specialfunctionswiki
The falling factorial $x^{\underline{k}}$ for nonnegative integer $k$ is given by $$x^{\underline{k}}=x(x-1)\ldots (x-k+1).$$
The falling factorial $x^{\underline{k}}$ for nonnegative integer $k$ is given by $$x^{\underline{k}}=x(x-1)\ldots (x-k+1).$$
