Definition:Rising Factorial

Definition

Let $x$ be a real number (but usually an integer).

Then the rising factorial with $n$ terms of $x$ is defined as:

$\ds x^{\overline n} := \prod_{j \mathop = 0}^{n - 1} \paren {x + j} = x \paren {x + 1} \cdots \paren {x + n - 1}$

This is also referred to as the $n$th rising factorial (power) of $x$.

It can also be referred to as the $x$ to the (power of) $n$ rising, hence the tempting phrase rising power.

The notation $x^{\overline n}$ for $x$ to the $n$ rising is due to Alfredo Capelli, who used it in $1893$.

This is the notation of choice on $\mathsf{Pr} \infty \mathsf{fWiki}$.

A more commonly seen notation (though arguably not as good) is $x^{\paren n}$.

This is known as the Pochhammer function or (together with $\paren x_n$ for its falling counterpart) the Pochhammer symbol (after Leo August Pochhammer).

However, depending on the context, either $\paren x_n$ or $x^{\paren n}$ can be used to indicate the rising factorial.

In the field of combinatorics $x^{\paren n}$ tends to be used, while in that of special functions you tend to see $\paren x_n$.

Therefore the more intuitively obvious $x^{\overline n}$ is becoming the preferred symbol for this.