Reciprocal of Riemann Zeta Function

From ProofWiki
Jump to navigation Jump to search

Theorem

For $\map \Re z > 1$:

$\ds \frac 1 {\map \zeta z} = \sum_{k \mathop = 1}^\infty \frac{\mu \left({k}\right)} {k^z}$

where:

$\zeta$ is the Riemann zeta function
$\mu$ is the Möbius function.


Proof

By Sum of Reciprocals of Powers as Euler Product:

\(\ds \frac 1 {\map \zeta z}\) \(=\) \(\ds \prod_{\text {$p$ prime} } \paren {1 - p^{-z} }\)
\(\ds \) \(=\) \(\ds \paren {1 - \frac 1 {2^z} } \paren {1 - \frac 1 {3^z} } \paren {1 - \frac 1 {5^z} } \paren {1 - \frac 1 {7^z} } \paren {1 - \frac 1 {11^z} } \cdots\)


The expansion of this product will be:

$\ds 1 + \sum_{\text {$n$ prime} } \paren {\frac{-1} {n^z} } + \sum_{n \mathop = p_1 p_2} \paren {\frac {-1} {p_1^z} \frac {-1} {p_2^z} } + \sum_{n \mathop = p_1 p_2 p_3} \paren {\frac {-1} {p_1^z} \frac {-1} {p_2^z} \frac {-1}{p_3^z} } + \cdots$

which is precisely:

$\ds \sum_{n \mathop = 1}^\infty \frac {\map \mu n} {n^z}$

as desired.



$\blacksquare$