# Definition:Riemann Zeta Function

## Definition

The Riemann Zeta Function $\zeta$ is the complex function defined on the half-plane $\map \Re s > 1$ as the series:

$\displaystyle \map \zeta s = \sum_{n \mathop = 1}^\infty \frac 1 {n^s}$

### Critical Strip

Let $s = \sigma + i t$.

The region defined by the equation $0 < \sigma < 1$ is known as the critical strip.

### Critical Line

Let $s = \sigma + i t$.

The line defined by the equation $\sigma = \dfrac 1 2$ is known as the critical line.

Hence the popular form of the statement of the Riemann Hypothesis:

All the nontrivial zeroes of the Riemann zeta function lie on the critical line.

## Analytic Continuation

By Analytic Continuations of Riemann Zeta Function, $\zeta$ has a unique analytic continuation to $\C \setminus \set 1$.

This analytic continuation is still called the Riemann zeta function and still denoted $\zeta$.

## Zeroes

The zeroes of the Riemann zeta function are, according to the conventional definition of the zero of a (complex) function, the points $s \in \C$ such that:

$\map \zeta s = 0$

### Trivial Zeroes

The trivial zeroes of the Riemann zeta function $\zeta$ are the strictly negative even integers :

$\set {n \in \Z: n = -2 \times k: k \in \N_{\ne 0} } = \set {-2, -4, -6, \ldots}$

### Nontrivial Zeroes

The nontrivial zeroes of the Riemann zeta function $\zeta$ are the zeroes of $\zeta$ that are not trivial.

## Also see

• Results about the Riemann $\zeta$ function can be found here.

## Source of Name

This entry was named for Georg Friedrich Bernhard Riemann.

## Historical Note

The Riemann zeta function was discussed by Bernhard Riemann in his $1859$ article Ueber die Anzahl der Primzahlen under einer gegebenen Grösse.

Studying it led Jacques Salomon Hadamard to his proof of the Prime Number Theorem.

All of the statements made in that paper have now been proved except for one.

The last remaining statement which has not been resolved is the Riemann Hypothesis.

When Riemann first investigated this function, he used $s$ instead of the more typical complex variable $z$.

To this day, $s = \sigma + i t$ is still typically used as the complex variable in investigations of the zeta function.