>>619-620
横レス失礼
検索ですぐ分かること、下記です
付け加えることがあれば、お願いします

google訳
”Χはディリクレ指標であり、s は1 より大きい実数部を持つ複素変数です。”
”証明の過程で、ディリクレは、L ( s , χ )がs = 1で非ゼロであることを示しました。さらに、χが主関数である場合、対応するディリクレL関数はs = 1で単純な極を持ちます。”

https://en.wikipedia.org/wiki/Dirichlet_L-function
Dirichlet L-function
a Dirichlet L-series is a function of the form
L(s,χ) = Σ_{n=1}^∞ {χ(n)}/{n^s}.
where
χ is a Dirichlet character and s a complex variable with real part greater than 1.
It is a special case of a Dirichlet series. By analytic continuation, it can be extended to a meromorphic function on the whole complex plane, and is then called a Dirichlet L-function and also denoted L(s, χ).

These functions are named after Peter Gustav Lejeune Dirichlet who introduced them in (Dirichlet 1837) to prove the theorem on primes in arithmetic progressions that also bears his name.
In the course of the proof, Dirichlet shows that L(s, χ) is non-zero at s = 1.
Moreover, if χ is principal, then the corresponding Dirichlet L-function has a simple pole at s = 1. Otherwise, the L-function is entire.