Questions on more advanced topics of number theory. Consider first if (elementary-number-theory) might be a more appropriate tag before adding this tag.

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2
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1answer
56 views

Hard Simultaneous Diophantine Equations

Find all positive integers $a,b,c,d,e,f$ such that : $de^2=ab^2+1$ and $df^2=ac^2+1$. I tried subtracting them, it factors quite nicely. But after that, haven't a clue. I'm not sure if it's even ...
2
votes
1answer
119 views

Are there any “obviously” true propositions in number theory?

After all efforts spent on wrong proofs of famous number theory conjectures and theorems like Goldbach's or Fermat's last theorem, could one find some simple statements (might be correct ones) whose ...
2
votes
3answers
97 views

Irrational number “test”?

Suppose we have a finite quantity $a$, which we would like to prove to be irrational, supposing that it is indeed irrational. Then, would it be enough to show that ...
0
votes
1answer
33 views

Counting points in/on cuboid

Given a cuboid that extend in x,y,z axis such that |x|≤N, |y|≤N, |z|≤N where N is given and can have value up to 10^9.Now a shooter is standing at origin (0,0,0).He need to shoot on any of the ...
1
vote
2answers
47 views

$a^2-b^2 = k$, $ab = l$ for fixed integer $k,l$ when $a,b$ are both integers

Let us fix integers $k,l$. Let all numbers be integers. Now we want integer $a,b$ to satisfy: $$a^2-b^2 = k, \,\,\,2ab = l.$$ We want to maximize the number of possible $(a,b)$. In order to do ...
22
votes
1answer
226 views

Which is greater, $20 \uparrow\uparrow\uparrow\uparrow 20$ or $4 \uparrow\uparrow\uparrow\uparrow\uparrow 4$?

This past Wednesday's What-If had this image at the bottom: In particular, I am interested in $20 \uparrow\uparrow\uparrow\uparrow 20$. I immediately thought of Graham's Number, but clearly that ...
3
votes
0answers
34 views

Generalization of small set/large set

A small set is a subset of the positive integers, such that the infinite sum of the reciprocals of the members of the set converges. Conversely, the sum of the reciprocals of a large set diverges. ...
2
votes
2answers
52 views

Can there ever be infinite number of tuples of $(a,b,c,d)$ such that $ac-bd = k$ and $ad+bc = l$ for fixed $k,l$?

Suppose, for now, that all numbers are real numbers. Let us fix numbers $k,l$. Then can there ever be infinite number of tuples of $(a,b,c,d)$ such that $ac-bd =k$, $ad+bc = l$ for some $k$ and $l$? ...
5
votes
1answer
76 views

On the square coeffecients of a modular form

Let $k\in \mathbb{N}$. Let $f\in M_k(\Gamma_0(N),\chi)$ be a modular form of weight $k$ on $\Gamma_0(N)$ with a Dirichlet character $\chi$. If $f$ has a Fourier expansion of the form $$ ...
0
votes
2answers
96 views

Modulus of large powers

Given an array of N integers where $2 ≤ N ≤ 2×10^5$ and each element in array is less than $10^{16}$. Now I am given a variable $X$ that can also go up to $10^{16}$. We need to find if $X \mid ...
0
votes
2answers
79 views

Find all non-trivial triplets $(a,b,c)$ such that $ a+b^{d}\equiv0\pmod c $ for all $d>0$

Let $a,b,c$ be co-prime integers $>2$ . Find all non-trivial triplets $(a,b,c)$ such that $ a+b^{d}\equiv0\pmod c $ for all $d>0$.
0
votes
1answer
63 views

Can anyone recommend an easy to read algebraic number theory book?

Can anyone recommend an easy to read algebraic number theory book ? I prefer a book with good examples. (hints or answers to selected questions if possible. Not sure if it is possible for a book of ...
12
votes
2answers
284 views

Why are people more interested in the Riemann hypothesis than Goldbach's conjecture? [closed]

One of my friends, a math professor, told me almost every one of his colleagues (in the math department) had attempted to prove the Riemann hypothesis at some point in their life (maybe secretly). ...
0
votes
1answer
38 views

Convergence of $\sum_{n=1}^{\infty} n$ and integral test [duplicate]

I have read online, that one can show that $\sum_{n=1}^{\infty}n = -\frac{1}{12}$. But isn't this a Riemann Series of the form $\sum_{n=1}^{\infty} \frac{1}{n^p}$, where $p=-1$. And if so, can't ...
3
votes
2answers
55 views

Which natural numbers can be represented as a sum of natural numbers raised to different powers?

Waring's problem asks about natural numbers that can be represented as a sum of natural numbers all raised to the same power $k$. I'm wondering which natural numbers can be represented as a sum of ...
4
votes
0answers
155 views

Prove modular equivalence related to carmichael function.

Statement if $n=p_1p_2p_3\cdots p_r$ (prime numbers are distinct) and $2 \le a \le n-1$ then prove that $$a^{k\lambda} \equiv \left(1+\sum_{p_i\mid\gcd(a,n)}\left(\dfrac{n}{p_i} \right) ...
1
vote
3answers
53 views

Rational numbers and periodic decimal representation

I'm trying to prove that a number is rational if and only if it has an eventually periodic decimal expansion. One part is simple; without loss of generality we consider $q=0.\overline{d_1\dots d_k},$ ...
3
votes
3answers
107 views

Upper bound for Euler's totient function on composite numbers

I've seen before the general bound $\phi(n) \leq n - n^{1/2}$ for composite $n$. Can this bound be improved at least for those $n$ when we don't have equality above? Say could we possibly have at ...
4
votes
1answer
79 views

Factoring numbers

I was given the following problem: Prove that 767, 76767, 7676767 ... are all composite. Making a sequence $a(n)$ = {767, 76767, 7676767, ...} you can show that $a(3k+1)$ is divisble by 13, ...
10
votes
2answers
203 views

Cubic polynomial equal to a cube

I've been researching cubes and I'm trying to solve this Diophantine equation over the integers. $$ax^3 + bx^2 + cx + d = y^3$$where a, b, c, d are parameters for a given $n$. For example, for $n = ...
0
votes
0answers
44 views

Diophantine Equations involving cubes

I'm doing some number theory research and I came across these two Diophantine equations (created under my own transformations): $$y^3 = ax^3 + bx$$ (where $a$ and $b$ are parameters) $$z^3 = x^2 + ...
1
vote
2answers
61 views

Why attempt to find 'b' in golden ratio ends up with odd results?

Imagine that you have a line segment which is divided into larger and smaller segment. You want to find a golden ratio for the longer segment $a$, and shorter one $b$. As you know the phi number which ...
2
votes
1answer
26 views

Using continued fractions to well-approximate a quadratic form?

Continued fractions are the "best rational approximation" of other numbers. For a real number $\alpha$ the continued fraction algorithm produces a sequence of integers $\alpha = [a_1, a_2, \dots, ...
6
votes
1answer
64 views

When does $(a^p-1)/(a-1)$ have a $p$th power factor?

Today I noted that $(18^3-1)/(18-1) = 343 = 7^3$, and that there are no other solutions to the equation $(a^3-1)/(a-1) = b^3$ with $b \le 100000$. There are, however, many solutions to the equation $$ ...
2
votes
0answers
28 views

floor function inequality $\frac{3c-3n-3}{2n+3} \geq \lfloor\frac{3c-3n}{2n+3}\rfloor$

I want to prove following statement: $$\forall K\in \mathbb R \exists c\in \mathbb N c\geq K s.t.\forall n\in \left\{1,2,...,c-1\right\}: \frac{3c-3n-3}{2n+3} \geq \lfloor\frac{3c-3n}{2n+3}\rfloor$$ ...
1
vote
1answer
12 views

Exponention cipher - prove unique mapping from plain text to cipher text

At the heart of RSA, is the exponention cipher: C=M^e mod P (where C=ciphertext, M=Plaintext e=exponent and P=modulus.) How do you prove that two different plaintexts don't map to same ciphertext?
0
votes
0answers
36 views

Hard Diophantine: $ xy-\frac{(x+y)^2}{n}=n-4 $

Solve in positive integers $x,y$: $ xy-\frac{(x+y)^2}{n}=n-4 $ $n>4$ is a given positive integer. I cannot even solve in the case $n=5$. I have been able to find $x,y$ and construct $n$ using ...
3
votes
2answers
121 views

Solving $x^3+y^3=x^2y^2+1$ in non-negative integers

I wanted to solve $x^3+y^3=x^2y^2+1$ in non-negative integers. First I set $a=x+y$ and $b=xy$ to get $b^2+3ab+1=a^3$. View as a quadratic in $b$, the discriminant = $4a^3+9a^2-4$, which needs to be a ...
0
votes
1answer
52 views

Solve for x,y: $x^2+1=2y^2$

Solve for integers $x,y$ such that $x^2+1=2y^2$? I tried factoring as $(x-y)(x+y)=(y-1)(y+1)$ but couldn't continue from here, I would appreciate any help. Thanks!
1
vote
0answers
59 views

Integer partitions without rotated solutions?

I'm searching for an algorithm to determine a list of all integer partitions of a number $n$ into a fixed number $m$ of summands (say $n=6$ and $m=4$), for instance to be stored into a list of ...
2
votes
1answer
40 views

How prove $n|2^{\frac{n(n-1)}{2}}\cdot (2-1)(2^2-1)(2^3-1)\cdots (2^{n-1}-1)$

Question: Today, when I solve other problem, I found this follow interesting result $$n\mid\left(2^{\frac{n(n-1)}{2}}\cdot (2-1)(2^2-1)(2^3-1)\cdots (2^{n-1}-1)\right),n\ge 1$$ It is clear ...
4
votes
2answers
73 views

Find a real numbers $a,b$ such $a^n+b^n$ is rational

Question: prove or disprove :there exsit real numbers $a,b$ such follow two condition: (1):$a+b$ is irrational (2): for any postive integer $n\ge 2$, then $a^n+b^n$ is rational. I have know if ...
2
votes
2answers
57 views

Diophantine: $px^2+2=y^2$ where $p\in \mathbb{P}$

Solve the Diophantine Equation: $px^2+2=y^2$, where $p$ is a prime number and $x,y$ integers. I tried this for ages but didn't get anywhere, but I don't know any advanced machinery since I am only in ...
0
votes
0answers
37 views

Twisting modular forms by Dirichlet characters

Let $\chi,\chi_1$ be Dirichlet characters modulo $M$ and $N$. In Koblitz's book "Introduction to Elliptic Curves and Modular Forms", Proposition III.3.17, it is proved that if ...
7
votes
1answer
70 views

What is $\limsup\limits_{n\rightarrow\infty}\left\{\frac{p_{m+1}}{p_m}|m\in \mathbb{N},m\geq n\right\} $?

What is $$\limsup\limits_{n\rightarrow\infty}\left\{\frac{p_{m+1}}{p_m}\middle|m\in \mathbb{N},m\geq n\right\} = ?$$ where $p_i$ is i'th prime number. We know that this limsup exists because of ...
0
votes
0answers
30 views

how to lift geometrically integralness using etale(+something else) morphisms

Take $X$ and $Y$ to be $k$-varieties, where $k$ is a field of characteristic 0. Assume also that $X$ is geometrically integral, and let $f: Y \to X$ be an etale a morphism of $k$-varieties. Question: ...
4
votes
0answers
87 views

Is it decidable whether the iterates of a polynomial map are bounded?

Let $f:\mathbb{Q}^n\to \mathbb{Q}^n$ be a polynomial map with rational coefficients. Let $p\in \mathbb{Q}^n$. Is there a known algorithm that given this data determines whether or not the iterates ...
0
votes
1answer
27 views

Representation of integers by ternary quadratic form $x^2+y^2-z^2$

Let $Q$ be the ternary quadratic form $Q(x,y,z)=x^2+y^2-z^2$. Since $Q(0,p+1,p)=2p+1$ and $Q(1,p+1,p)=2p+3$, we see that for every integer $k$, the equation $E_k:Q(x,y,z)=k$ always has a solution. Is ...
0
votes
2answers
35 views

Show that for all positive real numbers $a,b$, not both of $a(1-b),b(1-a)$ are greater than $\frac{1}{4}$

Question: Show that for all positive real numbers $a,b$, not both of $a(1-b),b(1-a)$ are greater than $\frac{1}{4}$ Attempt: I have attempted several things with this problem. I will note what ...
2
votes
0answers
76 views

Diophantine inequality that comes up after Vieta Jumping Hurwitz technique

I am blaming this on Prove the equality EDITTTTT: allowing $x_1 \geq x_2$ and $x_2 \geq x_n,$ I would rather not explain what that was about and the only changes are in $n=3,4,$ already settled. ...
1
vote
0answers
47 views

Fast checking Matrix multiplication in mod 10

I recently faced this problem in a programming contest: Given 3 square matrices N x N of size N up to 1000. All elements in 3 matrices are from 0 to 9. Check if matrix A x B equals to C, mod 10. In ...
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vote
0answers
62 views

sum of reciprocal power-1

I found this in my old notebook $$\sum_{n \text{ perfect power}} {\frac{1}{n-1}} = 1$$ and this was my "proof" $$ \begin{align} \frac{1}{1}+\frac{1}{2}+\cdots ...
4
votes
3answers
102 views

$ 1987 \mid \left( n^n + (n+1)^n \right) $

Problem from the 1987 Leningrad Math Olympiad: Is there a positive integer $n$ such that $ n^n + \left( n + 1 \right)^n $ is divisible by $ 1987 $? The provided solution: The answer is ...
0
votes
4answers
70 views

Number theory divisibility - simple way to prove this is prime?

Suppose that $y$ is a positive integer, and $z$ is the largest factor of $y$ such that $z<y$, then let $x=y/z$. Prove that $x$ must be a prime number. Is there a simple way to solve this? It ...
1
vote
0answers
13 views

Examples of the local Langlands correspondence

I'm trying to compile some examples of the local Langlands correspondence, with the aim of motivating the statement and also just giving some concrete traction on how it works. I would especially like ...
1
vote
1answer
40 views

A direct proof of $\binom{m\,p^k-1}{p^k-1}\equiv1~(\text{mod $p$})$?

In Nathan Jacobson's "Basic algebra I" the exercises 1.13.11-14 prove the following extension of (a part of) the Sylow's second theorem: If $p$ is a prime and $p^k\bigm||G|$, then the number of ...
1
vote
2answers
102 views

Property of set of prime numbers

let $\{p_1,p_2,p_2,\cdots ,p_r\}$ be the set of $r$($\ge2$) pair wise distinct prime numbers i.e.., $(i\ne j \implies p_i \ne p_j)$ for all $1\le i,j\le r$ ${Statement}$ : For any such ...
-2
votes
0answers
55 views

Number theory elementary

I am having a problem solving this: Given that $n$ is a non prime number, $\phi(n)$ is the Euler's totient function. I need to prove that if $\phi(n)\mid (n-1)$, then $n$ has at least $3$ distinct ...
1
vote
1answer
58 views

Algebraic groups of multiplicative type in char 0

For a number field $k$ (so of char 0), are algebraic $k$-groups of multiplicative type always linear?
0
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0answers
42 views

Number of prime factors of Mersenne numbers

Let $p$ be a prime and let $M_p = 2^p-1$. Is it known whether the number of prime factors of $M_p$ is unbounded above as $p \to \infty$? Also do the probabilities estimating the chance that $M_p$ is ...