For questions on Dirichlet series.

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On Dirichlet series and Firoozbakht's conjecture

On assumption of the Firoozbakht's conjecture (this is the Wikipedia, but the reference is for Carlos Rivera's Page) one has that can writes informally the Dirichlet series in LHS of this inequality $$...
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Multiplication of Dirichlet Series

here is the following theorem: "Given the two functions F(s) and G(s) represented by Dirichlet series with $L(s,f)=\sum_{n=1}^{\infty} \frac{f(n)}{n^s}$ for $\sigma>a$ and $L(s,g)=\sum_{n=1}^{\...
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Showing $L(1,\chi)$ is positive given that it's nonzero

Let me first provide context for this question. There is a series of four exercises in Ireland & Rosen's book (in second edition it's exercises 14-17 in chaprer 16), aim of which is (although ...
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45 views

Is there no proof of Dirichlet's results on quadratic residues without analysis?

Wikipedia states that all known proofs of Dirichlet's results $$ L(1) = -\frac{\pi}{\sqrt q}\sum_{n=1}^{q-1} \frac{n}{q} \left(\frac{n}{q}\right) \gt 0 $$ and $$ L(1) = \frac{\pi}{\left(2-\left(\...
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1answer
26 views

Can the coefficients of a Dirichlet series be recovered?

Specifically if I have a known function $F(s)$ is there some way I can find a function $f(n)$ that satisfies this equation? $$F(s) = \sum_{n=1}^\infty \frac{f(n)}{n^s}$$ I'm imagining something ...
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Is this Dirichlet series generating function of the von Mangoldt function matrix correct?

Let $\mu(n)$ be the Möbius function and let $a(n)$ be the Dirichlet inverse of the Euler totient function: $$a(n) = \sum\limits_{d|n} d \cdot \mu(d)$$ Let the matrix $T$ be defined as: $$T(n,k)=a(...
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L-series through integrals of rational functions

Recently I stumbled upon this short proof here: $$L(1,\chi_2)=\sum_{j=0}^{+\infty}\left(\frac{1}{3j+1}-\frac{1}{3j+2}\right)=\int_{0}^{1}\frac{1-x}{1-x^3}\,dx=\int_{0}^{1}\frac{dx}{1+x+x^2}$$ so: $$\...
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40 views

How do we evaluate this Dirichlet L-series

In this answer, David Speyer, whose answer is magnificent, states that "The sum $\sum \chi_3(n)/n$ is only slightly less well known; it is $\pi/(3 \sqrt{3})$.", where $\chi_3(n)$ is the character ...
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integrating a function of a dirichelet random vector on a subset

Consider a random vector $\bar{X}$ of n many variables $X_i \in (0,1)$ such that $\sum_{i=1}^{n}X_i = 1$ and let the sequence of $x_i$ be a random realization of $\bar{X}$. The distribution of $\bar{X}...
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Doubts and computations about Dirichlet series and aliquot sequences II

From previous post* dedicated to aliquot sequences I believe that I can state that for $\Re s>2$, on assumption that the Catalan-Dickson conjecture is false $$\sum_{n=1}^{\infty}\frac{s^{k+1}(n)-\...
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Doubts and computations about Dirichlet series and aliquot sequences I

Perhaps the more easier statement that one can deduce for aliquot sequences (which is the Wikipedia's Page) is the following Lemma. For an integer $n\geq 1$, let $s^0(n)\equiv n$, $s(n)\equiv s^1(...
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Mobius function related series and Dirichlet summation

A well known identities of rare beauty is that: $$\sum_{n=1}^\infty \frac{\mu(n)}{n^s}=\frac 1{\zeta(s)}$$ Where $\mu(n)$ is the Mobius function and $\zeta(s)$ is the Riemann Zeta function. So, in ...
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Proof of Dirichlet L-function Euler Product formula (from Fourier Analysis by Stein)

On page 260 of Stein and Shakarchi's "Fourier Analysis," there's a proof of the Dirichlet product formula: $\sum_{n}\frac{\chi(n)}{n^s}=\Pi_{p}\frac{1}{1-\chi(p)p^{-s}}$ where $s>1$, $\chi$ is a ...
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51 views

On a simple application of Paley-Wiener theorem and related doubts

Let $$F(x)=\frac{ \left\{ x \right\} }{e^{\sqrt{x}}},$$ be supported on $ \left( 0,\infty \right) $, where $ \left\{ x \right\} $ is the fractional part function. Then $F\in L^2(0,\infty)$ and the ...
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Dirichlet series decomposition of an arbitrary function

Analytic functions can be decomposed into a Taylor series, and furthermore the Taylor series converges back to the original function at every point. Is there a corresponding notion for Dirichlet ...
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Dirichlet series with abscissa of absolute convergence $= \frac{1}{2}$

I'm trying to figure out a Dirichlet series which has its abscissa of absolute convergence $=\frac{1}{2}$. I've been trying to think about using the formula for this abscissa: $$\sigma_a=\limsup_{n\...
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Convergence of the Euler product

Suppose that the Riemann Hypothesis is true. It is well known that then the Dirichlet series $$\sum_{n=1}^\infty\frac{\mu(n)}{n^s}$$ converges in the half-plane ${\rm {Re}}\, s>\frac{1}{2}$. Does ...
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1answer
35 views

Green function for Dirichlet-problem for $L=p(x)\frac{d^2}{dx^2}+q(x)\frac{d}{dx}+r(x)$

Let $G(x,\xi)$ be de Green function for the Dirichlet problem for $L=p(x)\frac{d^2}{dx^2}+q(x)\frac{d}{dx}+r(x)$, where $p\in C^2$, $q \in C^1$, $r \in C^0$ and $p(x)\neq 0$ for every $x \in [a,b]$. ...
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Analytic Dirichlet series

I have another question regarding Dirichlet series. This one is about where the Dirichlet series $f(s)=\sum_{n=1}^{\infty}\frac{a_{n}}{n^{s}}$ is analytic. I have the next theorem: "$f(s)$ is ...
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1answer
51 views

We can suppose without loss… General Dirichlet question

I would like to know why I can start supposing that $\sigma_{0}=0$ in the proof of the following theorem about Dirichlet series: "Let $a_{n}\ge0$ for every $n\ge1$. Then the point $s=\sigma_{0}$ is a ...
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1answer
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Are all series in the elementary Ramanujan class R = 1 non-summable by analytic continuation of Dirichlet series?

We say that a series $\sum_{n=1}^\infty a_n$ and the corresponding power series $f(x)=\sum_{n=1}^\infty a_nx^n$ belong to the Ramanujan class $R=1$ if $g(x)=f(x)-f(x^2)$ is Abel summable at $x=1$ (...
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Closed-form for $\sum_{n=2}^{\infty} \frac{1}{\pi (n)^2}$

Is there a closed form for $$\sum_{n=2}^{\infty} \frac{1}{\pi (n)^2}$$ (where $\pi (x)$ is the number of primes less than or equal to x)? It's obvious that $$\sum_{n=2}^{\infty} \frac{1}{\pi (n)^s}$$ ...
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Dirichlet clustering and group assignment

As in the Dirichlet clustering, the dirichlet process can be represented by the following: Chinese Restaurant Process Stick Breaking Process Poly Urn Model For instance, if we consider ...
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1answer
55 views

Does the Abel sum 1 - 1 + 1 - 1 + … = 1/2 imply $\eta(0)=1/2$?

If $\sum_{n=1}^\infty a_n$ is Abel summable to $A$, then necessarily $\sum_{n=1}^\infty a_n n^{-s}$ has a finite abscissa of convergence and can be analytically continued to a function $F(s)$ on a ...
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A linear operator that extends the summation of Dirichlet series

Consider a vector space $\mathcal{V}$, a linear operator $L$ and a vector subspace $\mathcal{A}$ such that for all $x\in\mathcal{A}$ $Lx\in\mathcal{A}$ and for a number $R\neq0,1$ $R^{-1}$ is not a ...
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1answer
52 views

What's the function that is related to 3 as the Riemann zeta function is related to 2?

For $f(x)=\sum_{n=0}^\infty a_n x^n$, a real number $R\neq 1$, $g(x)=f(x)-Rf(x^2)$ Abel summable at $x=1$, $g(1)=\lim_{x\to 1^-} g(x)$, the elementary Ramanujan sum of $f(x)$ at $x=1$ is defined by $f(...
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if $f(x)$ is periodic $\left|\int_1^\infty f(x) x^{-s} dx\right| \sim C\left|\int_1^\infty \sin(x) x^{-s} dx\right|$ when $\text{Im}(s) \to \infty$

is it true that if $f(x)$ is periodic, non-constant and bounded $$\text{when } T \to \infty ,\qquad\qquad\sup_{|t| \ <\ T}\ \ \left|\ \int_1^\infty f(x) x^{-\sigma-it} dx\ \right| \ \sim \ ...
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Exploring the Dirichlet series of the sum of remainder function

I wolud like to learn and understand more some basic facts about Dirichlet series, for wich I want explore the following function, that is called the sum of remainders function, A004125 as Sloane's ...
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Is the limit of a Dirichlet series to infinity always equal to the constant term?

Given a sequence of complex numbers $(a_n)$ one defines the corresponding Dirichlet series as $$f(s) = \sum_{n = 1}^\infty \frac{a_n}{n^s}.$$ I know that there is some $x_0 \in \mathbb{R} \cup \{\pm \...
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2answers
51 views

Determining the coefficients of the reciprocal of a Dirichlet series

Given a Dirichlet series with coefficients $$ F(s)= \sum_{n=1}^{\infty}\frac{a(n)}{n^{s}},$$ is it then always possible (and how) to obtain the $ b(n) $ coefficients related to its reciprocal $$ \...
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178 views

Product of two series to get a series decomposition of zeta in the critical strip

$\def\sfrac#1#2{% \small#1% \kern-.05em\lower0.1ex/\kern-.025em% \lower0.4ex\small#2}$I've been working on gaining an intuitive understanding of the analytic continuation of the zeta ...
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Uniform and ordinary convergence of a series.

I have a series of the kind $\sum\limits_{n=1}^{\infty} \frac{a_nt^n}{1+t^{2n}}$, $t\in(0,\infty)$. Btw, $a_n$ are real and they are determined by several integrals, but it is possible to compute any ...
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Are these two naive upper bounds ok?

EDIT: Is my work ok? Here, I am trying to show a uniform bound for the sum of $cos(n)$ $$|\sum_{n=1}^{N} cos(n)|$$ $$=\big |\sum \frac{e^{in} + e^{-in}}{2}\big|$$ $$\le \sum |\frac{e^{in} + e^{-in}...
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1answer
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Can be justified this formula for $\zeta(2n+1)$

Can be justified for integers $n\geq 1$ that $$\zeta(2n+1)=\prod_{\text{p, prime}}\frac{1-\sigma(p^{2n})^{-1}}{1-p^{-2n}}?$$ Truly I don't know if I am wrong another time, when I use for an integer $...
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On a generalization for $\sum_{d|n}rad(d)\phi(\frac{n}{d})$ and related questions

Let $\phi(m)$ Euler's totient function and $rad(m)$ the multiplicative function defined by $rad(1)=1$ and, for integers $m>1$ by $rad(m)=\prod_{p\mid m}p$ the product of distinct primes dividing $...
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Dirichlet series with logs&zeta function

i have the following question: Let F(s) be the Dirichlet series associated to $$f(n)= \sum_{d|n} \frac{log(d)}{d} $$. My answer has to depend on the zeta function. (i.e simplify F(s) so that we can ...
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Absolute convergence of ordinary Dirichlet series

I am currently reading Serre's 'A course in Arithmetic' and I have a question about proposition 8 of section 2.4 (but I think the question can be answered without knowing the book.) The proposition ...
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Proof that $\int f(x)\sin(Nx)\ dx \to 0$ as $N \to \infty$

I'm studying Fourier series out of Rudin's "Principals of Mathematical Analysis". In the proof that the Fourier series $s_N(f;x)$ converges pointwise to $f$, it assumes that at a point $x$, there is ...
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Average Order of $\frac{1}{\mathrm{rad}(n)}$

Again a question about $\mathrm{rad}(n).$ Let $\mathrm{rad}(n)$ denote the radical of an integer $n$, which is the product of the distinct prime numbers dividing $n$. Or equivalently, $$\mathrm{rad}(...
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64 views

Having some trouble using Dirichlet's test to show series convergence,

The series is $$\sum_{k=1}^{\infty} \frac{1}{k^\alpha}\log\left(1+\frac{1}{k}\right)$$ Since the summand is a product of two factors, and the log factor is monotonically decreasing to zero, as n goes ...
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What is the use of Dirichlet Integral? [closed]

How can I find the value of $$\large\int_0^\infty\left(\dfrac{\sin x}x\right)^5dx$$ using Contour Integrals? I attempted it using Integration by Parts and got the an got the answer. I have studied ...
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Partial GCD - Sum

$\sum\limits_{n = 2}^{M} \sum\limits_{m = 1}^{R} GCD(m,n) $ $R = (\lfloor\dfrac{N}{n}\rfloor-n) \% n $ $M = \lfloor\sqrt{N}\rfloor $ I calculated that - For N=10 the sum is 1 For N = 100 the ...
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Multiplicative function and Euler product

Theorem 1 Let $G \subset \mathbb{C}$ be an area and $\sum_{n=1}^{\infty}a_n e^{-\lambda _ns} $ and $\sum_{n=1}^{\infty}b_n e^{-\lambda _ns} $ two Dirichlet-series that converge on $G$ and represents ...
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Is series $\displaystyle\sum^{\infty}_{n=1}\frac{\cos(nx)}{n^\alpha}$, for $\alpha>0$, convergent?

I've done the following exercise: Is series $\displaystyle\sum^{\infty}_{n=1}\frac{\cos(nx)}{n^\alpha}$, for $\alpha>0$, convergent? My approach: We're going to use the Dirichlet's ...
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64 views

show that there are infinitely many primes congruent to 1 or 4 modulo 5…

Given the following Dirichlet character: $\epsilon (n)=\begin{Bmatrix} 1 : n\equiv 1,4(mod 5)\\ -1 : n\equiv 2,3(mod 5) \end{Bmatrix}$ It is known that it is multiplicative, i.e $\epsilon(nm) = \...
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Dirichlet kernel [duplicate]

Can anybody help me please in showing that $$\dfrac{1}{2} + \sum_{k = 1}^{N} \cos(kx) = \dfrac{\sin\left(N + \dfrac{1}{2}\right)}{2\sin\dfrac{x}{2}}$$ please?
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1answer
100 views

How does Dirichlet regularization of $1 + 2 + 3 + …$ work?

How does Dirichlet regularization assign value $-1/12$ to $\sum_{k=1}^{\infty} k$? Yes, I know that $\zeta(-1) = - 1/12$, a result that follows from the Riemann functional equation $\zeta(s) = 2^s \...
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1answer
65 views

Dirichlet series expansion for Zeta(s)

Wikipedia lists a series expansion for $\zeta(s)$ here. How is the Dirichlet series below derived? I apologize in advance if this is a very simple question, I don't know much about Dirichlet series. ...
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Integral evaluation for the Riesz means special case $s_n=1$

At the moment, I am investigating the Riesz means defined as the series $$ s^{\delta}(\lambda)=\sum_{n\leq\lambda}\left( 1-\frac{n}{\lambda} \right)^{\delta}s_n. $$ Consider the special case $s_n=1$. ...
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Prove or disprove the existence of f(k) when $\sum_{n=1}^m{\frac{a_n}{n^s}}=\sum_{n=1}^m\frac{a_n+f^n(x)}{n^s}$.

Can we find a function, $f(k)$, such that $$\frac{a_n}{n^s}+\frac{a_{n+1}}{(n+1)^s}+\frac{a_{n+2}}{(n+2)^s}=\frac{a_n+x}{n^s}+\frac{a_{n+1}+f(x)}{(n+1)^s}+\frac{a_{n+2}+f(f(x))}{(n+2)^s}$$ for some $x$...