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8 votes
4 answers
870 views

A cubic equation, and integers of the form $a^2+32b^2$

I am trying to determine whether there are any integers $x,y,z$ such that $$ 1+2 x+x^2 y+4 y^2+2 z^2 = 0. \quad\quad\quad (1) $$ It is clear that $x$ is odd. We can consider this equation as quadratic ...
Bogdan Grechuk's user avatar
4 votes
2 answers
709 views

On the product $\prod_{k=1}^{(p-1)/2}(x-e^{2\pi i k^2/p})$ with $x$ a root of unity

Let $p$ be an odd prime. Dirichlet's class number formula for quadratic fields essentially determines the value of the product $\prod_{k=1}^{(p-1)/2}(1-e^{2\pi ik^2/p})$. I think it is interesting to ...
Zhi-Wei Sun's user avatar
  • 15.6k
4 votes
0 answers
238 views

On the values of $\prod_{k=1}^{(p-1)/2}(e^{2\pi i/12}-e^{2\pi i k^2/p})$ for primes $p>3$

In a recent preprint, I investigated $$S_p(x):=\prod_{k=1}^{(p-1)/2}(x-e^{2\pi ik^2/p}),$$ where $p$ is an odd prime and $x$ is a root of unity. Motivated by Question 337879 and Question 338325, ...
Zhi-Wei Sun's user avatar
  • 15.6k
3 votes
1 answer
233 views

Pythagorean triples and quadratic residues modulo primes

QUESTION. Are my following conjectures true? How to prove them? Conjecture 1. For each prime $p>100$, there are $a,b,c\in\{1,\ldots,p-1\}$ such that $$\left(\frac ap\right)=\left(\frac bp\right)=\...
Zhi-Wei Sun's user avatar
  • 15.6k
2 votes
1 answer
197 views

Mod n, are all higher powers also lower powers?

Since there are only finitely many residues mod $n$, there is some function $H(n) \le n$ such that for all integers $n>1$, $r$, and $e>H(n)$, if $r$ is an $e$-th power mod $n$ then there is some ...
Charles's user avatar
  • 9,114