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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 ...

5 votes
1 answer
493 views

Nice diophantine equations with large smallest solutions

Given a polynomial $P$ with integer coefficients in finitely many variables, we denote by $v(P)$ the product of the absolute values of the non-zero coefficients and the non-zero total degrees of the m …
8 votes
Accepted

The exponential Diophantine equation $a^n-b^m=x^3+y^3$ for arbitrary large $n,m$

We have the following polynomial identity: $$ 3^{12k+6} - b^{24\ell} \ = \ (3^{3k+2} b^{2\ell} - b^{8\ell})^3 + (3^{4k+2} - 3^{k+1} b^{6\ell})^3. $$ Therefore Question 1 …
Stefan Kohl's user avatar
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2 votes

Equation $x^2=y^p + 1$

For $t = 1$, your question is about a special case of Catalan's conjecture, which has been proved in 2002 by Preda Mihăilescu. In particular, for $t = 1$ the only solution is $3^2 = 2^3 + 1$.
Stefan Kohl's user avatar
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38 votes
Accepted

Does the equation $241+2^{2s+1}=m^2$ have a solution?

To answer your first question: there is indeed no $s$ such that $241+2^{2s+1}$ is a perfect square. -- Proof: $2^{2s+1}$ is always congruent to either $2$, $8$ or $32$ modulo $63$, which makes $241+2^ …
Stefan Kohl's user avatar
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24 votes
1 answer
2k views

Algorithmic (un-)solvability of diophantine equations of given degree with given number of v...

Question: For which $d, k \in \mathbb{N}$ is there an algorithm to determine whether a polynomial diophantine equation $$ P(x_1, \dots, x_k) = 0, \ \ \ P \in \mathbb{Z}[x_1, \dots, x_k] $$ …
Stefan Kohl's user avatar
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6 votes

Algorithm for solving systems of linear Diophantine inequalities

GAP provides a function NullspaceIntMat which solves systems of linear diophantine equations. The documentation says: 25.1-2 SolutionIntMat * SolutionIntMat( mat, vec ) ───────────────────────────── …
Stefan Kohl's user avatar
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30 votes
5 answers
3k views

Parametric solutions of Pell's equation

Given a positive integer $n$ which is not a perfect square, it is well-known that Pell's equation $a^2 - nb^2 = 1$ is always solvable in non-zero integers $a$ and $b$. Question: Let $n$ be a posit …
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4 votes
0 answers
206 views

Monte Carlo variant of Hilbert's Tenth Problem

Let $k \in \mathbb{N}$. Given an algorithm $\mathcal{A}$ which takes as argument a polynomial $P \in \mathbb{Z}[x_1,\dots,x_k]$ and either returns true or false, we say that $\mathcal{A}$ works for $P …
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10 votes

On Generalizations of Fermat's Conjecture

The smallest counterexample for $n = 4$ is $95800^4 + 217519^4 + 414560^4 = 422481^4$. This has been found out by Roger Frye in 1988, cf. http://euler.free.fr/docs/euler88.ps.
Stefan Kohl's user avatar
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14 votes

Is there an algorithm to solve quadratic Diophantine equations?

Let me just add that for solving quadratic diophantine equations in 2 variables, i.e. equations of the form $$ ax^2 + bxy + cy^2 + dx + ey + f = 0, \ \ a, b, c, d, e, f \in \mathbb{Z}, $$ there is a …
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