Questions tagged [arithmetic-functions]
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76
questions
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Write large $n$ as $n_1+\ldots+n_k\ (n_1<\ldots<n_k)$ with $\varphi(n_1),\ldots,\varphi(n_k)\in\{x^k:\ x\in\mathbb Z\}$
Let $\varphi$ denote Euler's totient function.
QUESTION. Is it true that for each positive integer $k$ large integers $n$ can be written as $n_1+\ldots+n_k$ with $n_1,\ldots,n_k$ distinct positive ...
0
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0answers
66 views
On the equation that involves the Dedekind psi function $\psi(x)=n$ with unique solution $x$, for a fixed integer $n\geq 1$
The Dedekind psi function is defined for a positive integer $m>1$ as
$$\psi(m)=m\prod_{\substack{p\mid m\\p\text{ prime}}}\left(1+\frac{1}{p}\right)\tag{1}$$
with the definition $\psi(1)=1$. See ...
0
votes
2answers
110 views
What is the dirichlet series of $f(n)=\sum_{d | n}(\log d) / d$ function? [closed]
My opinion is ;
We may use id(d)=d arithmetic function and log*id dirichlet convolution in the question.
i thought that ; when we multiply and divide n with $(\log d) / d$ we obtain
$F(S)=\sum_{n=...
0
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0answers
160 views
When is $\phi(a^n+b^n+c^n)=0\mod n$?
A corollary Zsigmondy's Theorem leads to the following congruence (one can look to $(24)$),$\phi(a^n+b^n)=0\mod n$ whenever $a, b$ are coprime and $n \neq 2$ and $(a,b)\neq(1,1)$. (Here $\phi$ is the ...
1
vote
1answer
121 views
Bounds for two arithmetic functions, when one assumes that $n$ are odd perfect numbers
For an integer $n>1$ in this post we denote the Dedekind psi function as $\psi(n)=n\prod_{\substack{p\mid n\\p\text{ prime}}}\left(1+\frac{1}{p}\right)$ and the product of distinct primes dividing ...
2
votes
1answer
219 views
Is there a smallest $r$ such that $n+\varphi(n)=\displaystyle \prod_{i=1}^r q_i$ always has solutions for mutually different odd primes $q_i $?
While discussing with Peter in one of the chatrooms on MSE I proposed an idea to try to find smallest natural number $r$ such that $n+\varphi(n)=\displaystyle \prod_{i=1}^r q_i$ has solutions for ...
0
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0answers
71 views
Set of primes $p_{1}\equiv 3 \bmod p_{2}$ such that $\phi(2^{\frac{{p_1}-3}{p_2}}-1)\equiv 0 \bmod p_1$ with $p_1,p_2\equiv 3\bmod 4$?
let $p_1$ and $p_2$ be positive primes such that $p_1,p_2 \equiv 3\bmod 4$
and $\phi$ is the Euler totiont function , I want to find the Set of primes $p_{1}\equiv 3 \bmod p_{2}$ such that $\phi(2^...
2
votes
0answers
219 views
If some numbers satisfy this divisibility condition with $\sigma$ and $\varphi$, are they necessarily multiples of $6$?
After doing some computations of the divisibility of $\sigma(n)$ by $n+ \varphi(n)$, mostly with Peter´s help, we found these solutions:
$n=2, 456, 828, 7584 ,33462 , 1357440, 1596048 ,1964544 ,...
13
votes
0answers
380 views
Is this arithmetic function strictly positive and unbounded?
As requested by Mathphile, since there have been efforts but no complete solutions to some questions raised when this question was asked on MSE, and since we think that here the question is more ...
7
votes
1answer
332 views
How to explain this property of totient?
I am running a program to search for solutions of $$\varphi(pm+1)=\varphi(pm+p+1).$$
So far, for $m=1,\ldots,327$ solutions have been found (some relatively large).
(in the body of the question, $p$ ...
0
votes
0answers
127 views
Given $\,m=\prod_k {p_k}^{\alpha_k}\,$ and the function $\,g(m)=\sum_k \alpha_k(p_k-1)^2$, find all solutions of the equation $\,g(2n)=n$
Let's consider the unique decomposition of a natural number $\,m\,$ into its prime factors:
$$\prod_k {p_k}^{\alpha_k}$$
Then, let's define the following arithmetic function (completely additive) $\,g:...
5
votes
1answer
148 views
The asymptotic of $|\{1\leq n\leq x|\gcd(n,S(n))=1\}|$, with $S(n)$ the sum of remainders, and get idea for other miscellany problem
Let $n\geq 1$ be an integer. In this post we denote the sum of remainders function as $$S(n)=\sum_{k=1}^n n \bmod k,$$ for example $S(1)=S(2)=0+0$ and $S(5)=0+1+2+1+0=4$. In the literature there are ...
1
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0answers
41 views
On a type of equations that involve certain multiplicative functions and polynomials, in relation to their number of solutions
Past weekend I was interested in the sequence A058891 from the On-Line Encyclopedia of Integer Sequences, from this, inspired by the equation due to Benoit Cloitre (2002) that shows the comments, I ...
0
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0answers
183 views
On an inequality involving the Lambert $W$ function and the sum of divisors function
Let $W(n)$ be the principal/main branch of the Lambert $W$ function (this is the Wikipedia related to this special function). I was inspired in Robin equivalence to the Riemann hypothesis (see [1]) ...
1
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0answers
67 views
Alternating series of arithmetic function values
Some time ago I asked about alternating sums like
$\sum_{n\leq x}(-1)^n \phi(n)$ where $\phi(n)$ is Euler's totient
and the similar sum involving $\sigma(n)$ where $\sigma(n)=\sum_{d|n}d.$
Certain ...
0
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0answers
60 views
Prove that the Mertens function is invariant under matrix inversion for $n>3$
Consider the lower triangular matrix $T$ with the definition:
$n \leq3 :$
$$T(n, 1)=1$$
$n>3:$
$$T(n,1)=x_n$$
$n \geq k:$
$n \leq 3:$
$$T(n,k)=1$$
$n \geq k:$
$n>3:$
$k=2 \text{ or } k=3:$
...
8
votes
0answers
155 views
Strong uniqueness of Euler's totient function
Let $f:\mathbb N\to \mathbb C$ be some arithmetical function. Define $\varphi_f(n)$ by the following formula:
$$
\varphi_f(n)=\sum_{\substack{k\leq n \\ (k,n)=1}}f(k).
$$
In other words, $\varphi_f(...
4
votes
1answer
378 views
A curious conjecture: $\{\varphi(m^2)/\varphi(n^2):\ m,n=1,2,3,\ldots\}=\{r>0:\ r\in\mathbb Q\}$
Let $\varphi$ denote Euler's totient function. It is easy to see that all those numbers
$$\varphi(n^2)=n\varphi(n)\ \ (n=1,2,3,\ldots)$$
are pairwise distinct.
I have the following surprising ...
2
votes
0answers
74 views
$\varphi(m+n)\mid n$ for some positive integer $n$
Let $\varphi$ be Euler's totient function.
If $p$ is a prime, then $\varphi(1+n)=n$ for $n=p-1$.
Question. Is it true that for each integer $m>1$ there is a positive integer $n\le m^2-m$ such that ...
5
votes
0answers
214 views
Can we write each positive integer as $x^2+y^2+\varphi(z^2)$?
As odd squares are congruent to $1$ modulo $8$, any integer of the form $4^k(8m+7)$ with $k,m\in\mathbb N=\{0,1,2,\ldots\}$ cannot be written as the sum of three squares.
To avoid such congruence ...
9
votes
1answer
608 views
Is the sum $\sum_{d\mid n}\frac1{d+1}$ never integral?
Recall that a positive integer $n$ is a perfect number if and only if
$$\frac{\sigma(n)}n=\sum_{d\mid n}\frac1d=2.$$
QUESTION: Is my following conjecture true?
Conjecture. (i) We have $\sum_{d\mid ...
2
votes
0answers
61 views
Uniformity in Wirsing's Mean Value Theorems
In two important papers of Wirsing, namely "Das asymptotische Verhalten von Summen über multiplikative Funktionen" (1961) and its follow up (1967), several results on mean values of multiplicative ...
6
votes
2answers
2k views
Does this multiplicative function have a name? If so, what is known about it?
It is well-known that the Euler $\phi$-function is multiplicative: that is, for co-prime positive integers $m,n$ we have $\phi(mn) = \phi(m)\phi(n)$. Thus it is defined by its values on prime powers. ...
10
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0answers
933 views
Euler's totient function and Riemann hypothesis
I am looking for an upper-bound of the Euler's totient function $\varphi$ which would be equivalent to the Riemann hypothesis (RH). There is the following Nicolas' criterion about primorial numbers $...
3
votes
0answers
120 views
Is there a way to reduce this problem to two variables through functions coming from arithmetic?
Consider following diophantine equation in $\mathbb Z[x,y,z]$ in three integer variables $x,y,z$
$$x^2+L(y,z)x+L_1(y)L_2(z)=0$$ where $L(y,z)$ is a non-homogeneous linear polynomial in $y,z$ and $L_1(...
4
votes
1answer
380 views
A conjecture regarding odd perfect numbers
(Note: I asked this question in MSE this June 2018 but did not receive any responses there. I have therefore cross-posted it here, hoping that it gets answered.)
Let $\sigma(z)$ denote the sum of ...
asked Sep 19 '18 at 7:44
Jose Arnaldo Bebita-Dris
1,3242 gold badges10 silver badges29 bronze badges
8
votes
1answer
358 views
Goldbach's conjecture for the Liouville function
Is it true that for every even integer $N > 2$, there exist positive integers $a,b$ such that $a + b = N$ and $\lambda(a) = \lambda(b) = -1$ ?
Here $\lambda$ is the Liouville function.
4
votes
1answer
151 views
The number of solutions of the equation $ax_1x_2+by_1y_2=n$
The equation $x_1x_2+y_1y_2=n$ is well-studied (Ingham, Heath-Brown, Deshouillers & Iwaniec, Ismoilov) because it arises in an additive divisor problem. The number of solutions in positive ...
4
votes
1answer
435 views
Reference for inequality for $\sum\limits_{d \mid n}\frac{\log d}{d}.$
Let $f(n)=\sum\limits_{d \mid n}\frac{\log d}{d}.$
It is not hard to see that $f(n)\ll(\log\log n)^2$. Is there any reference for this inequality?
EDT 1: A possible answer is Analysis of the ...
1
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0answers
145 views
Primes approximated by eigenvalues?
Let the matrix $T$ be defined by:
$$\displaystyle T(n,k) = -\varphi^{-1}(\operatorname{GCD}(n,k))$$
where $\varphi^{-1}$ is the Dirichlet inverse of the Euler totient function.
$$\varphi^{-1}(n) = \...
7
votes
1answer
352 views
On $\varphi(m)\varphi(n)\equiv0\pmod{m+n}$
Euler's totient function $\varphi$ is multiplicative, and it plays important roles in number theory.
QUESTION: Is it true that for each integer $m>6$ we have $\varphi(m)\varphi(n)\equiv0\pmod{m+n}$...
1
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0answers
89 views
Existence of equation about the product of the divisor sum function
Let $\sigma_k(n)$ be the sum of the $k$-th powers of the positive divisors of $n$ and $\mu(n)$ be the Möbius function.
As Arithmetic function - Wikipedia mentioned, there is an equation that $$\...
1
vote
1answer
250 views
The Euler's totient function and the product of distinct primes dividing $n$ versus the Heronian means
For integers $n\geq 1$ with $$\operatorname{rad}(n)=\prod_{\substack{p\mid n\\p\text{ prime}}}p$$ we denote the squarefree kernel or radical of an integer $n$ (see if you want this Wikipedia). And $\...
3
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0answers
140 views
Is there a closed form for the discrete convolution of $\sigma_1$ and $\sigma_2$?
I am trying to find a closed form for the following sum:
$$\sum_{k = 1}^{n-1}\sigma_1(k) \sigma_2(n-k)$$
where $\sigma_i$ is the sum of divisors and $\sigma_2$ is the sum of squares of divisors.
...
11
votes
3answers
423 views
Evaluating the sum of $kl^2$ over $p,q,k,l$ such that $pk +ql = n$
I have come across the following sum:
$$\sum_{\substack{p, q, k, l \in \mathbb{N} \\ k > l \\ pk + ql = n}}kl^2$$
and I am trying to simplify it, hoping to get a nice formula in terms of $n$ and ...
4
votes
1answer
303 views
A special kind of multiplicative function $f: \mathbb N \to \mathbb N$ such that $f(p)=p+k$ for all odd prime $p$, where $k>1$ is a fixed odd integer
For which odd positive integer $k$, can we find a multiplicative function $f: \mathbb N \to \mathbb N$ satisfying the following conditions :
$f(p)=p+k$ for all large enough odd prime $p$ and the set $...
0
votes
0answers
84 views
Name and theory of multi-valued functions $F:\mathbb{N}^k \rightarrow \mathbb{N}^l$
In computability theory there are considered mostly single-valued functions $f:\mathbb{N}^k \rightarrow \mathbb{N}$. (Let $\mathbb{N}$ be a placeholder for $\mathbb{N}$ or any initial segment $[0,n]$ ...
1
vote
1answer
136 views
Tighter upper bound for $\sum_{i=1}^kA_i\log(\frac{A_i}{e})$
What is the tightest upper bound one can obtain for the following expression
$$\sum_{i=1}^kA_i\log(\frac{A_i}{e})$$ subject to $\sum_{i = 1}^k A_i = C$ in terms of $C$ and $k$?
A very loose upper ...
6
votes
1answer
347 views
The importance of relations between automorphic forms and arithmetic functions
As I understand things, one of the classical reasons to care about modular forms was their relation to interesting arithmetic functions/counting questions, i.e. on sums of squares and partitions. When ...
13
votes
2answers
961 views
A mystery sequence
This question arose from the recent one, roots of a polynomial linked to mock theta function?. Let
$$
g(x):=\sum_{k=0}^\infty x^k\prod_{j=1}^{k-1}(1 + x^j)^2\\=1+x+x^2+3 x^3+4 x^4+6 x^5+10 x^6+15 x^7+...
0
votes
0answers
181 views
Representation of a number as a sum of co-prime numbers
Conventions
We will call the following product the canonical expansion of $a$:
$$a = \prod\limits_{p_i\in\mathbb{P}}p_i^{\alpha_i}.$$
If $a$ and $b$ are co-prime we write
$$a \perp b.$$
$\beth$-...
1
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0answers
83 views
An arithmetic function involving arbitrary (but fixed) number of divisors
I need at least basic information about generating functions of the following class of arithmetic functions, grouped by levels $k$.
Fix some $k$ and some family $\varepsilon_*=(\varepsilon_\sigma)_{\...
4
votes
2answers
254 views
Congruences for the non-divisors of Euler's $\phi(n)$
If $n$ is composite, then $\phi(n) < n-1$: hence, there is at least one number $d$ which does not divide $\phi(n)$ but divides$(n-1)$. We shall call $d$ the totient divisor of $n$. The purist will ...
3
votes
0answers
139 views
Mersenne number with small Carmichael function
Let $\lambda(\cdot)$ be the Carmichael function. I'm trying to understand the magnitude of the smallest values of $\lambda(2^n - 1)$, when $n$ runs over the positive integers. Precisely my question is:...
17
votes
2answers
906 views
Does 53 diverge to infinity in this Collatz-like sequence?
This function has been explored a bit at MSE (in June 2016):
\begin{eqnarray}
f(n) &=& (n-1)^2 \; \textrm{if} \; (n \bmod 4) = 1\\
f(n) &=& \lfloor n/4 \rfloor \; \textrm{otherwise}
\...
5
votes
1answer
341 views
Does anyone recognize this exponential sum?
For $a$, $b$ two integers, let $(a,b)$ denotes their gcd. We define the following exponential sum :
$$G_q(n):=\sum_{d|q,~(d,q/d)=1}{e^{2i\pi n\frac{dd'}{q}}}$$
for $n$ a non-negative integer and $q$ ...
4
votes
0answers
238 views
The properties of Pos
Given $n\in\mathbb{N}$, and $f:\mathbb{N}^*\rightarrow \mathbb{N}$, let define $Pos$ as:
$$Pos(f)(n)= |\{x \leq n, f(x)=f(n)\}|$$
When given $n\in\mathbb{N}$, this function gives the 'position' of $...
1
vote
0answers
242 views
On even almost perfect numbers other than powers of two
(Note: This question is an improved version of and has been cross-posted from this MSE post.)
Let $\sigma(x)$ denote the sum of the divisors of $x$. If $\sigma(x) = 2x - 1$, then we call $x$ an ...
asked Apr 7 '16 at 14:50
Jose Arnaldo Bebita-Dris
1,3242 gold badges10 silver badges29 bronze badges
8
votes
2answers
552 views
Asymptotics of product of Euler's totient function (A001088)?
Conjecture:
\begin{align}
\lim_{n\to \infty } \, \frac{\left(\prod _{k=1}^n \phi (k)\right){}^{1/n}}{n}\sim 0.2059\text{...}
\end{align}
The numerical result from 100000 terms is:
My questions are:
...
4
votes
2answers
474 views
Are there multiplicative functions which are not rational?
Vaidyanathaswamy calls an arithmetic function rational if it is the convolution of some finite collection of functions which are either completely multiplicative or inverse to a completely ...
