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Diophantine equations are polynomial equations $F=0$, or systems of polynomial equations $F_1=\ldots=F_k=0$, where $F,F_1,\ldots,F_k$ are polynomials in either $\mathbb{Z}[X_1,\ldots,X_n]$ of $\mathbb{Q}[X_1,\ldots,X_n]$ of which it is asked to find solutions over $\mathbb{Z}$ or $\mathbb{Q}$. Topics: Pell equations, quadratic forms, elliptic curves, abelian varieties, hyperelliptic curves, Thue equations, normic forms, K3 surfaces ...

4 votes

Integer solutions to $x^2 + x + 1 = y^z$?

You should definitely take a look at this previous answer of mine: https://mathoverflow.net/a/251637/1593
José Hdz. Stgo.'s user avatar
7 votes
3 answers
603 views

Question on a crucial lemma in Euler's approach to Fermat's Last Theorem for $n=3$

As many of you may know, the illustrious L. Euler put forward a proof of the case $n=3$ of Fermat's Last Theorem via infinite descent. The thing is that, at a certain point, he resorted to the follo …
José Hdz. Stgo.'s user avatar
2 votes

Perfect powers in the solutions of a certain Pell equation

I consider that an answer for the second question is recurrence relations for solutions of Pell's equations. In point of fact, by resorting to them I am going to prove below the OP's original conjectu …
José Hdz. Stgo.'s user avatar
6 votes
2 answers
700 views

Origin and variations of problem on $4xy-x-y$ being square

One of the forms in which the Diophantine equation in question can be found in the literature is this: Solve the equation \begin{eqnarray}z^{2} = 4xy-x-y \qquad \qquad (\ast)\end{eqnarray} in positi …
José Hdz. Stgo.'s user avatar
10 votes
Accepted

Solve this diophantine equation: $m^4+n^4=10m^2n^2+1$

You have already listed all the possible solutions $(m,n)$ in which either $m=0$ or $n=0$. Let us suppose that $(m,n) \in \mathbb{N} \times \mathbb{N}$ is a solution of your equation. Then, the discr …
José Hdz. Stgo.'s user avatar
9 votes
1 answer
679 views

On the exact reference of a cute Diophantine problem

The problem asks to prove that the Diophantine equation $x^{3}+y^{3} = (x+y)^{2}+(xy)^{2}$ does not have any solutions in natural numbers $x, y$. I believe that this problem appeared in the section За …
José Hdz. Stgo.'s user avatar
41 votes

Is $x^2+x+1$ ever a perfect power?

Your equation can be rewritten as $$\frac{x^{3}-1}{x-1} = y^{N}.$$ As Gerhard Paseman commented above, the Diophantine equation $$ \frac{x^{n} − 1}{x-1} = y^{q} \quad x > 1, \quad y>1, \quad n>2 \quad …
José Hdz. Stgo.'s user avatar
16 votes

Diophantine equation $3^n-1=2x^2$

W. Ljunggren proved in 1 that the Diophantine equation $$\frac{x^{n}-1}{x-1} = y^{2}$$ doesn't admit solutions in integers $x>1, y>1, n>2$, except when $n=4, x=7$ and $n=5, x=3$. Since your equation …
José Hdz. Stgo.'s user avatar
5 votes

Trost's Discriminant Trick

As I was browsing through the problems & solutions department of the American Mathematical Monthly the other day, I found out that, in his solution to problem E-2332 [1972, 87], which was published on …
José Hdz. Stgo.'s user avatar
20 votes
2 answers
2k views

On a result attributed to W. Ljunggren and T. Nagell

I've read in a number of places that, building on previous work of T. Nagell, W. Ljunggren proved in 1 that the Diophantine equation $$\frac{x^{n}-1}{x-1} = y^{2}$$ doesn't admit solutions in intege …
José Hdz. Stgo.'s user avatar