For questions on arithmetic functions, a real or complex valued function $f(n)$ defined on the set of natural numbers.

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1answer
78 views

how to prove $f$ is an arithmetic function with this property $\sum_{d\mid n} f(d)=n^2$

how to prove $f$ is an arithmetic function with this property $$\sum_{d\mid n} f(d)=n^2$$ Arithmetic function
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1answer
93 views

Solving $ f(\log x)$

A generalization of the conjecture $$\pi(x+x^{\theta}) - \pi(x) \sim \frac{x^\theta}{\log x} $$ (Ingham, 1937 or earlier) might be $$\Delta \pi_k = \pi_k((x+1)^2) - \pi_k(x^2)\sim \frac{x}{\log ...
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1answer
55 views

Prime Factorization and Number Theory

Prime factorization of $n$ is $$n = p_1^{a_1}p_2^{a_2}p_3^{a_3}\cdots p_k^{a_k}$$ Let $f(n) = p_1^{e_1}p_2^{e_2}p_3^{e_3}\cdots p_k^{e_k}$ where $e_k=a_k$ if $p_k|a_k$, else $e_k=a_k-1$ I want to ...
2
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1answer
51 views

Arithmetic function

An arithmetic function is defined as follows:$f(1)=1$, $f(2k)=k$ and $f(2k+1)=f(k)+f(k+1)$. When (for which $k$) is $f(k)$ even? While it is obvious that $f(4n-1)=f(4n)=2n$, therefore $f(k)$ is even ...
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0answers
75 views

Smallest prime p with N a quadratic residue mod p

Let $N$ be a square-free number equal to 2 or 3 $(\mod 4)$. Let $P(N)$ be the first odd prime, not a factor of $N$, for which $N$ is a quadratic residue. On average, $N$ would be a non-residue for ...
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0answers
69 views

Approximate how the Numbers $n$ such that Mertens' function is zero grow.

Is it possible to approximate how the "Numbers $n$ such that Mertens' function is zero" grow?
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5answers
207 views

For every positive integer n greater than $2$, $\phi(n)$ is an even integer.

Theorem: For every positive integer n greater than $2$, then $\phi(n)$ is an even integer. I know this theorem and the same is used much, but I was curious how it would be to demonstrate it, show ...
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3answers
144 views

Are there any integer solutions to $\gcd(\sigma(n), \sigma(n^2)) = 1$ other than for prime $n$?

A good day to everyone! Are there any integer solutions to $\gcd(\sigma(n), \sigma(n^2)) = 1$ other than for prime $n$ (where $\sigma = \sigma_1$ is the sum-of-divisors function)? Note that, if $n = ...
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2answers
75 views

Is Wiki wrong on Dirichlet Chararcters Modulo $10$?

Wiki says: Modulus 10 There are $\phi(10)=4$ characters modulo $10$. Note that $χ$ is wholly determined by $\chi(3)$, since $3$ generates the group of units modulo $10$. I can ...
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2answers
572 views

Infinitely many positive integers $n$ such that $\phi(n) = \frac{n}{4}$?

Do there exist infinitely many positive integers $n$ such that $\phi(n) = \dfrac{n}{4}$?
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1answer
50 views

Evaluate $\sum_{d\mid N}\Lambda(d)$

For a positive integer $n$, define $$\Lambda(n) = \left\{ \begin{array} {ll} \log p & \mbox{if $n = p^r$, $p$ a prime and $r \in \mathbb{N},$ }\\ 0 & \mbox{otherwise.} ...
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2answers
69 views

About the 'sigma' function.

Is it true that if $n$ divides $m$ , $\sigma(\frac mn) \leq \frac{\sigma(m)}n$. If so this has a bearing on counterexamples to Robin's inequality.
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2answers
109 views

If $(m,n)=1$ then $m^{\phi(n)}+n^{\phi(m)}\equiv0\pmod {mn}$

Show that if $(m,n)=1$ then $m^{\phi(n)}+n^{\phi(m)}\equiv0\pmod {mn}$ I tried, $(m,n)=1$ then, Euler theorem we have $m^{\phi (n)}\equiv1\pmod n$ and $n^{\phi (m)}\equiv1\pmod m$. But I could ...
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1answer
199 views

How can the Möbius function be applied to a series?

Given a series $p_n(s)=\sum_{k=1}^n a_k $. I'd like to get $\hat{p}_n(s)=\sum_{k=1}^n \mu(k)a_k $. Think of $a_k=k^{-s}$ for example. If you let $n$ go to $\infty$, you'll see the well-known relation ...
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2answers
41 views

Finding root for the segment - found the formula but it doesn't work for some values - wrong formula?

I have the segment, defined as $(x_1, y_1)$, $(x_2, y_2)$. I know that $y_1\ge 0$ and $y_2 < 0$. I want to compute the root point for that segment. I decided to do it that way: ...
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1answer
37 views

Demonstration in arithmetic function

I need help to know (in detail) how to prove that the product of two multiplicative arithmetic functions is a multiplicative arithmetic function. $$$$$f(n)$ and $g(n)$ are functions multiplicative, ...
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1answer
240 views

Function that counts the number of divisors of a natural number?

Let Function $f(n)$ be formally defined for natural numbers such that it gives number of distinct divisors of the number n (n and 1 included) For example, $f (12)=6$, then what is a quick way to ...
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1answer
68 views

Finding formulas for sums

I know that $\sum_{d \mid n} \mu(d) = 0$ whenever $n >1$, and I know that $\sum_{d \mid n} \phi(d) = n$. How can I use this in order to give a formula for $\sum_{d \mid n} \mu(d)\phi(d)$?
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2answers
24 views

Mean of given Arithmetic function

Find the mean of $a, a+d, a+2d, a+3d,\dots,a+nd$ I have no idea what to do in this question but i have tried the following: $$mean\ \bar{x}= \frac{(a)+(a+d)+(a+2d)+(a+3d)+\cdots+(a+nd)}{n+1} $$ ...
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1answer
57 views

Farey Sequence Vector Orthogonality Relation Question

Take the Farey sequence $\mathcal{F}_n$ for $n=39$ with values $a_m\in \mathcal{F}_n$ and put them into a vector $$ \vec v_k=\biggr(\exp(2\pi i k a_m)\biggr)_m $$ Since Merten's function for $n=39$ ...
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1answer
73 views

What proportion of the natural numbers satisfy the following inequalities?

Let $\sigma_1(n)$ be the sum of the divisors of $n \in \mathbb{N}$, and let $$I(n) = \frac{\sigma_1(n)}{n}$$ be the abundancy index of $n$. What proportion of the natural numbers satisfy the ...
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1answer
115 views

Attempted exercise using Littlewood's theorem

This was an exercise to try to show we can use Littlewood's theorem$^1$ to prove that $$\lim_{N \to \infty}\frac{1}{N}\sum_{n=1}^{N} \frac{g(n)}{\log p_n} = 1 \hspace{30mm}(1)$$ If $\vartheta(p_k) ...
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1answer
147 views

Littlewood's 1914 proof relating to Skewes' number

From Littlewood's 1914 theorem (paraphrase): I propose to show there are arbitrarily large values of x for which successively $\psi(x) - x < - K\sqrt{x}\log\log\log x \tag{A}$ $ ...
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0answers
32 views

Proving an identity involving the product of the Möbius function and Euler’s totient function.

Could anyone kindly help me to prove that $$ \sum_{d|n} \mu(d) \varphi(d) = 0 $$ for all even integers $ n \geq 2 $, where $ \mu $ is the Möbius function and $ \varphi $ is Euler’s totient function? ...
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0answers
19 views

gcd of product of exponents of prime factors and product of prime factors

Let $n = \prod\limits_i p_i^{k_i}$. I want to express $$ \gcd(\prod\limits_i k_i, \prod\limits_i p_i) $$ as an arithmetic function (i.e get rid of gcd). Is that possible? Thanks!
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0answers
54 views

A challenge question in elementary number theory!

Find an expression for the following sum: $$\sum_{i:(i,n)=1}(i-1,n)$$ I guess that this sum equals to $\phi(n)d(n).$
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0answers
49 views

sum over primes involving divisor function (variation of the Titchmarsh divisor problem)

Does there exist an asymptotic estimate for the following sum over primes $$ \sum_{p\leq x} \frac{\tau(p-1)}{p}\;, $$ where $\tau(n)=\sum_{d|n}1$ is the divisor function?
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1answer
54 views

How to show that $f(p^{k}) = f(p) \cdot f(p^{k-1}) \Longrightarrow f(p^{k}) = [f(p)]^{k}$ [closed]

If f is an arithmetic function such that $f (1) = 1$ and $p$ is a prime number. Prove that: $\forall k \in \mathbb{N}$ $f(p^{k}) = f(p) \cdot f(p^{k-1}) \Longrightarrow f(p^{k}) = [f(p)]^{k}$
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0answers
26 views

All all hypo-multiplicative functions linear combinations of quasi-multiplicative functions?

A function $f(n)$ is multiplicative if, for all coprime $m$ and $n$, $f(m)f(n)=f(mn).$ It is called quasi-multiplicative by many authors if $f(m)f(n)=f(1)f(mn)$, and the two coincide when $f(1)=1.$ ...
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0answers
38 views

Multiple Dirichlet convolutions

I have been playing around with Dirichlet convolutions. As a reminder, take two arithmetic functions $f,g$, then their Dirichlet convolution is defined as the arithmetic function with: $(f\star g)(n) ...
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1answer
45 views

Sums involving square of Moebius function

I try to estimate the following sum: $$ \sum_{n \leq x}\mu(n)^2 f(n) $$ where $\mu(n)$ is a Moebius function and $f(n)$ is some multiplicative arithmetic function. If I understand it correctly it is ...
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0answers
20 views

An inequality involving Möbius function [duplicate]

For any positive integer $n$ show the inequality holds : $$\left|\sum_{i=1}^{n}\frac{\mu(i)}{i}\right|\le 1$$ I tried induction. when $\mu(n+1)=0$ it is trivial. But what if $\mu(n+1)\ne 0$? I am ...
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0answers
59 views

Summation of no. of divisors

Let $d(n)$ = no. of divisors of $n$ and $(d(n))^2$ = square of no. of divisors of n. Let $$S(N) = \sum_{n=1}^{N} d(n)$$ and $$S_2(N) = \sum_{n=1}^{N}(d(n))^2$$ $$S(N) = ...
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1answer
37 views

Arithmetic progressions that generate an infinite number of powers of 2?

For an arithmetic progression of the form $a_i = ki, i \in \mathbb{N}$, the question is trivial - if $k$ is a power of 2, then the progression will generate an infinite number of powers of 2, and no ...
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0answers
115 views

Generalizing a result on sums involving Euler's function

Motivation: It's known that there is a constant $0<K$ such that for any natural number $N$, $KN\leq \frac{\varphi(1)}{1}+\frac{\varphi(2)}{2}+\cdots+\frac{\varphi(N)}{N}$ (with $\varphi$ being ...
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2answers
59 views

Are there particular techniques to find the general formula for an arithmetic function, neither multiplicative nor additive?

I was reading about the Euler phi function and the sigma function when I began to wonder how on earth one gets to the general formula for an arithmetic function. I'm not considering trivial formulae ...
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2answers
21 views

Find the numbers; Arithmetic Progression.

The sum of four consecutive numbers in an A.P is $28$. The product of the second and third numbers exceeds that of the first and last by $18$. Find the numbers. I thought of this: $$S_{4} = ...
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1answer
91 views

Question about the proof of Theorem 2.19 (Page 38) of the book Introduction to Analytic Number Theory by Apostol

At the last line of the proof: $\lambda^{-1}(n)=\mu(n)\lambda(n)=\mu^2(n)=|\mu(n)|$. Why $\mu(n)\lambda(n)=\mu^2(n)$? How to prove this?
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1answer
47 views

Find the term of the G.P.

Find the term of the G.P. $1, 1.2, 1.44, 1.728,... $ which is just greater than $100$. Please somebody explain me the question? All i know is $a=1$ and $r=1.2$ Help :( should it be $T_{n} > ...
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1answer
17 views

how to check arithmetic progression of triangle

I solved the problem with the following text: In a rectangle the sides and the diagonal are an arithmetic progression. Calculate the circumference of the rectangle where the longer side is 44 cm ...
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1answer
41 views

A more elegant version of this function?

I challenged myself. The goal was to find a function $f$ with two variables $x$ and $y$ real, which results $1$ if $x=y$ and results $0$ if $x ≠ y$. But, the fonction can only use additions, ...
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1answer
88 views

What proportion of the positive integers satisfy $I(n) < \frac{2n}{n + 1} \leq I(n^2)$ < 2?

Let $$I(x) = \frac{\sigma(x)}{x}$$ be the abundancy index of the positive integer $x$. Note that $\sigma(x)$ is the classical sum-of-divisors function. For example, $$\sigma(12) = 1 + 2 + 3 + 4 + ...
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0answers
17 views

Number of triples $(a, b, c)$ with $1 \leq a,b,c \leq n$ which are coprime ($gcd(a,b,c)=1$)

Number of ordered triples $(a, b, c)$ with $gcd(a, b, c) = 1$ and $1 \leq a, b, c \leq n$ can be computed using the following formula: $$ C(n) = \sum_{k=1}^n\mu(k) \left \lfloor \frac{n}{k} \right ...
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0answers
42 views

What is the inverse of $f(x)=x^{x^x}$?

I'm curious to find the inverse of $ f(x)=x^{x^x} $ As an added extra, I'm already familiar with the Lambert Product Log function.
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0answers
29 views

Number of excellent pairs is equal to $\sigma(n)$

Let $\nu$ be an irrational positive number, and let $m$ be a positive integer. A pair of $(a,b)$ of positive integers is called good if $$a \left \lceil b\nu \right \rceil - b \left \lfloor a \nu ...
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1answer
47 views

Product of all divisors

Prove that $\prod_{d \mid n}d=n^{v(n)/2}$ where $v(n)$ is the sum of divisors function. We have if $n=p_{1}^{a_{1}}p_{2}^{a_{2}} \dots p_{k}^{a_{k}}$ then $v(n)=(a_{1} +1)(a_{2}+1) \dots (a_{k} ...
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0answers
57 views

Does there exist a counterexample to the inequality $I(n) < 2{\left(\frac{n}{n + 1}\right)}^2$, if $n$ is odd and deficient?

If $n$ is odd and deficient, does there exist a counterexample to the inequality $$I(n) < 2{\left(\frac{n}{n + 1}\right)}^2,$$ where $$I(x) = \frac{\sigma(x)}{x}$$ is the abundancy index of ...
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0answers
141 views

Can an odd perfect number be divisible by 101?

Preamble - This question is an offshoot from the following earlier questions here at MSE: Can an odd perfect number be divisible by 825? Can an odd perfect number be divisible by 165? Odd perfect ...
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1answer
94 views

Converting loop to a closed form expression? [duplicate]

Possible Duplicate: How to convert this loop into a closed form expression? I have the following code in Python ...
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5answers
143 views

Solve for $m\in\mathbb{N}$ the equation $\phi (m)=12$

Solve for $m\in\mathbb{N}$ the equation $\phi (m)=12$ I found (by trial) $m=\{13,21,26,28,36\}$, but do not know if misinterpreted the problem, but actually I suppose I have to find an equation ...