Rising factorial ($(a{)}_n=a(a+1)\cdots (a+n-1)$)

For a nonnegative integer $n$, the rising factorial is the product of $n$ consecutive increments starting at $a$, with $(a{)}_0=1$. Another notation is $a^{\overline{n}}$; the falling factorial uses descending factors. It compactly expresses the coefficient recurrence of a confluent hypergeometric function of the first kind.