Do there exist 100 positive distinct integers such that a cube of one of them equals the sum of the cubes of all the others? Mikhail Evdokimov
Problem
Source: 42nd International Tournament of Towns, Junior A-Level P5, Fall 2020
Tags: number theory, Tournament of Towns
20.02.2023 01:10
I am about to lose my mind... I asked ChatGPT this question and here is what it gave me as the answer: EDIT. It is wrong.
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20.02.2023 01:33
And this is why AI has long way to go The answer is assertive, and follows from my post here. For completeness, I replicate it below, where I do the proof for all $N\ge 4$: I claim there exists $a_1<\cdots<a_N$ such that \[ a_N^3 = \sum_{1\le i\le N-1}a_i^3. \]When $N=4$, $3^3+4^3+5^3 = 6^3$ and when $N=5$, $2^3 + 3^3 + 8^3 + 13^3 = 14^3$, settling $N\in\{4,5\}$. Now, if $a_1<\cdots<a_N$ satisfies the property then \[ (3a_1)^3 + \cdots + (3a_{N-1})^3 + (4a_N)^3 + (5a_N)^3 = (6a_N)^3, \]giving an example for $N+2$. From here, we complete the proof by induction.
20.02.2023 02:17
That is a relief The answers that ChatGPT generates are written with such assertion and certainty that it can easily deceive the reader if they are not careful. This was the first time I asked it a math question and when I saw it writing math formulas in LaTeX so fluently I was mesmerized! Thank you @grupyorum for your solution. I read the ChatGPT answer again and the formula $100a_k^3=\sum_{i=1}^{100}a_i^3\leq S$ does not make any sense.
20.02.2023 10:39
$11^3+12^3+13^3+\ldots +109^3=330^3$