>>622 補足

ディリクレ、PGL (1837)。「Beweis des Satzes、dass jede unbegrenzte arithmetische Progression、deren erstes Glied und Differenz ganze Zahlen ohne gemeinschaftlichen Factor sind、unendlich viele Primzahlen enthält」

Riemann zeta 1859か（下記）。ディリクレL函数が後だと思っていたが、逆だった
Riemann zetaで s = 1では、the harmonic series（調和級数）になり、”a simple pole at s = 1 with residue 1”ね
これ、ディリクレのL函数のs = 1と同じ

https://en.wikipedia.org/wiki/Riemann_zeta_function
The Riemann zeta function or Euler–Riemann zeta function, denoted by the Greek letter ζ (zeta), is a mathematical function of a complex variable defined as
ζ (s)=Σ_n=1〜∞ 1/n^s=1/1^s+1/2^s+1/3^s+・・・
for Re(s)>1, and its analytic continuation elsewhere.[2]
The Riemann zeta function plays a pivotal role in analytic number theory, and has applications in physics, probability theory, and applied statistics.
Leonhard Euler first introduced and studied the function over the reals in the first half of the eighteenth century.
Bernhard Riemann's 1859 article "On the Number of Primes Less Than a Given Magnitude" extended the Euler definition to a complex variable, proved its meromorphic continuation and functional equation, and established a relation between its zeros and the distribution of prime numbers.
This paper also contained the Riemann hypothesis, a conjecture about the distribution of complex zeros of the Riemann zeta function that many mathematicians consider the most important unsolved problem in pure mathematics.[3]

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