Euclid NT

by Taco12, Oct 6, 2023, 12:50 AM

Find all pairs of positive integers $(a,b)$ such that \[ a^2b-1 \mid ab^3-1. \]
Calvin Wang
This post has been edited 1 time. Last edited by Taco12, Oct 6, 2023, 12:50 AM

Pair of multiples

by Jalil_Huseynov, May 17, 2022, 6:44 PM

Find all pairs $(a,b)$ of positive integers such that $a^3$ is multiple of $b^2$ and $b-1$ is multiple of $a-1$.

IMO 2016 Shortlist, N6

by dangerousliri, Jul 19, 2017, 4:31 PM

Denote by $\mathbb{N}$ the set of all positive integers. Find all functions $f:\mathbb{N}\rightarrow \mathbb{N}$ such that for all positive integers $m$ and $n$, the integer $f(m)+f(n)-mn$ is nonzero and divides $mf(m)+nf(n)$.

Proposed by Dorlir Ahmeti, Albania

Floor of square root

by v_Enhance, May 3, 2013, 8:08 PM

Determine all positive integers $n$ for which $\dfrac{n^2+1}{[\sqrt{n}]^2+2}$ is an integer. Here $[r]$ denotes the greatest integer less than or equal to $r$.

IMO Shortlist 2011, Number Theory 3

by orl, Jul 11, 2012, 10:27 PM

Let $n \geq 1$ be an odd integer. Determine all functions $f$ from the set of integers to itself, such that for all integers $x$ and $y$ the difference $f(x)-f(y)$ divides $x^n-y^n.$

Proposed by Mihai Baluna, Romania

USAMO 1983 Problem 2 - Roots of Quintic

by Binomial-theorem, Aug 16, 2011, 9:50 PM

A=b

by k2c901_1, Mar 29, 2006, 11:15 AM

Let $a$, $b$ be positive integers such that $b^n+n$ is a multiple of $a^n+n$ for all positive integers $n$. Prove that $a=b$.

Proposed by Mohsen Jamali, Iran

USAMO 2001 Problem 5

by MithsApprentice, Sep 30, 2005, 8:14 PM

Let $S$ be a set of integers (not necessarily positive) such that

(a) there exist $a,b \in S$ with $\gcd(a,b)=\gcd(a-2,b-2)=1$;
(b) if $x$ and $y$ are elements of $S$ (possibly equal), then $x^2-y$ also belongs to $S$.

Prove that $S$ is the set of all integers.

IMO ShortList 1998, number theory problem 1

by orl, Oct 22, 2004, 2:59 PM

Determine all pairs $(x,y)$ of positive integers such that $x^{2}y+x+y$ is divisible by $xy^{2}+y+7$.
Attachments:
This post has been edited 2 times. Last edited by orl, Oct 23, 2004, 12:38 PM

IMO ShortList 2002, number theory problem 6

by orl, Sep 28, 2004, 1:11 PM

Find all pairs of positive integers $m,n\geq3$ for which there exist infinitely many positive integers $a$ such that \[ \frac{a^m+a-1}{a^n+a^2-1}  \] is itself an integer.

Laurentiu Panaitopol, Romania
Attachments:
This post has been edited 6 times. Last edited by orl, Sep 27, 2005, 4:59 PM

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