Falling and rising factorials

In mathematics, the Pochhammer symbol introduced by Leo August Pochhammer is the notation (x)_n, where n is a non-negative integer. Depending on the context the Pochhammer symbol may represent either the rising factorial or the falling factorial as defined below. Care needs to be taken to check which interpretation is being used in any particular article. Pochhammer himself actually used (x)_n with yet another meaning, namely to denote the binomial coefficient .