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Linear recurrence fits with factorial finitely often
Assassino9931   2
N Today at 8:12 AM by Assassino9931
Source: Bulgaria Balkan MO TST 2025
Let $k\geq 3$ be an integer. The sequence $(a_n)_{n\geq 1}$ is defined via $a_1 = 1$, $a_2 = k$ and
\[ a_{n+2} = ka_{n+1} + a_n \]for any positive integer $n$. Prove that there are finitely many pairs $(m, \ell)$ of positive integers such that $a_m = \ell!$.
2 replies
Assassino9931
Yesterday at 10:25 PM
Assassino9931
Today at 8:12 AM
Rational Number Theory
Olympiadium   11
N Yesterday at 1:15 PM by whwlqkd
Source: KJMO 2022 P8
Find all pairs $(x, y)$ of rational numbers such that $$xy^2=x^2+2x-3$$
11 replies
Olympiadium
Oct 29, 2022
whwlqkd
Yesterday at 1:15 PM
Stereotypical Diophantine Equation
Mathdreams   2
N Apr 6, 2025 by grupyorum
Source: 2025 Nepal Mock TST Day 2 Problem 1
Find all solutions in the nonnegative integers to $2^a3^b5^c7^d - 1 = 11^e$.

(Shining Sun, USA)
2 replies
Mathdreams
Apr 6, 2025
grupyorum
Apr 6, 2025
An easy 3 variable equation
BarisKoyuncu   6
N Apr 4, 2025 by Burak0609
Source: Turkey National Mathematical Olympiad 2022 P4
For which real numbers $a$, there exist pairwise different real numbers $x, y, z$ satisfying
$$\frac{x^3+a}{y+z}=\frac{y^3+a}{x+z}=\frac{z^3+a}{x+y}= -3.$$
6 replies
BarisKoyuncu
Dec 23, 2022
Burak0609
Apr 4, 2025
Junior Balkan Mathematical Olympiad 2024- P3
Lukaluce   13
N Apr 3, 2025 by EVKV
Source: JBMO 2024
Find all triples of positive integers $(x, y, z)$ that satisfy the equation

$$2020^x + 2^y = 2024^z.$$
Proposed by Ognjen Tešić, Serbia
13 replies
Lukaluce
Jun 27, 2024
EVKV
Apr 3, 2025
solve in Z: xy = 3 (x+y)-1
parmenides51   5
N Mar 31, 2025 by fruitmonster97
Source: Greece JBMO TST 2008 p4
Product of two integers is $1$ less than three times of their sum. Find those integers.
5 replies
parmenides51
Apr 29, 2019
fruitmonster97
Mar 31, 2025
Israel Number Theory
mathisreaI   62
N Mar 31, 2025 by cursed_tangent1434
Source: IMO 2022 Problem 5
Find all triples $(a,b,p)$ of positive integers with $p$ prime and \[ a^p=b!+p. \]
62 replies
mathisreaI
Jul 13, 2022
cursed_tangent1434
Mar 31, 2025
Hard number theory
Hip1zzzil   13
N Mar 30, 2025 by Hip1zzzil
Source: FKMO 2025 P6
Positive integers $a, b$ satisfy both of the following conditions.
For a positive integer $m$, if $m^2 \mid ab$, then $m = 1$.
There exist integers $x, y, z, w$ that satisfies the equation $ax^2 + by^2 = z^2 + w^2$ and $z^2 + w^2 > 0$.
Prove that there exist integers $x, y, z, w$ that satisfies the equation $ax^2 + by^2 + n = z^2 + w^2$, for each integer $n$.
13 replies
Hip1zzzil
Mar 30, 2025
Hip1zzzil
Mar 30, 2025
weird looking system of equations
Valentin Vornicu   37
N Mar 30, 2025 by deduck
Source: USAMO 2005, problem 2, Razvan Gelca
Prove that the system \begin{align*}
x^6+x^3+x^3y+y & = 147^{157} \\
x^3+x^3y+y^2+y+z^9 & = 157^{147}
\end{align*} has no solutions in integers $x$, $y$, and $z$.
37 replies
Valentin Vornicu
Apr 21, 2005
deduck
Mar 30, 2025
k Factorials, Sum of Powers, Diophantine Equations,
John_Mgr   3
N Mar 27, 2025 by John_Mgr
Source: Nepal NMO 2025 p4
Find all the pairs of positive integers $n$ and $x$ such that: \[1^n+2^n+3^n+\cdots +n^n=x!\]
$Petko$ $Lazarov, Bulgaria$
3 replies
John_Mgr
Mar 15, 2025
John_Mgr
Mar 27, 2025
a