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The falling factorial $$(x)_n$$ is defined as $$x \cdot (x - 1) \cdot (x - 2) \cdot \ldots \cdot (x - (n - 1))$$.[1]

## Examples

$$(x)_0$$ = 1
$$(x)_1$$ = x
$$(x)_2$$ = x(x-1)
$$(n)_n$$=n!