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Counterexample to Euler's conjecture on sums of like powers

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Re: Counterexample to Euler's conjecture on sums of like powers

#11

The recent counterexample to Fermat's Last Theorem was pretty interesting, too. 434437^15 + 588129^15 = 588544^15 https://www.google.com/search?q=588129%5E15+%2B+434437%5E15+...

Obviously a floating point error. But that's a fun demonstration of a bug in Google's calculator.

Re: Counterexample to Euler's conjecture on sums of like powers

#12

This is great from so many angles. The counterexample is solid mathematics, the paper is wonderfully to the point, and the use of computers to successfully investigate a pure math problem was innovative. I only wish they'd described the method they used to find the counterexample.

One could probably start with the fact that the last 2 digits of any 5th power are in "0, 1, 7, 24, 25, 32, 43, 49, 51, 57, 68, 75, 76, 93, 99" and go from there.

Re: Counterexample to Euler's conjecture on sums of like powers

#13
post #10

The recent counterexample to Fermat's Last Theorem was pretty interesting, too. 434437^15 + 588129^15 = 588544^15 https://www.google.com/search?q=588129%5E15+%2B+434437%5E15+...

No? 434437¹⁵ + 588129¹⁵ = 352114612798389918432959038931874707477944791745072116429171623348641601872653349744942 588544¹⁵ = 352114612798389919037509191076162751408804961099244071160111294752887772695040228327424 It’s apparently close enough to fool Google, but it’s not correct.

~10^-18 difference as a fraction of the latter power [0], but still a substantially huge number (on the order of 10^68) [1].

[0] https://www.wolframalpha.com/input/?i=588129%5E15+%2B+434437...

[1] https://www.wolframalpha.com/input/?i=(+588129%5E15+%2B+4344...

Re: Counterexample to Euler's conjecture on sums of like powers

#14

This is great from so many angles. The counterexample is solid mathematics, the paper is wonderfully to the point, and the use of computers to successfully investigate a pure math problem was innovative. I only wish they'd described the method they used to find the counterexample.

they probably used the meet in the middle technique: http://www.infoarena.ro/blog/meet-in-the-middle

Re: Counterexample to Euler's conjecture on sums of like powers

#15
A fine example of the fact that brute force is often a powerful heuristic. I believe I recall hearing from the MIT OCW Algorithms course that they often rely on computer time doing exhaustive search (i.e. brute force) to "not disprove" some algorithm they develop before sinking too much time into developing a mathematical proof.

Re: Counterexample to Euler's conjecture on sums of like powers

#16

This is great from so many angles. The counterexample is solid mathematics, the paper is wonderfully to the point, and the use of computers to successfully investigate a pure math problem was innovative. I only wish they'd described the method they used to find the counterexample.

As a first attempt, I guess you'd create a table of 5th powers of integers through (say) 1000, then look for combinations of two, three, or four entries from the same array that added up to one of the same numbers. Or more likely, walk through the array and subtract all combinations of one, two, three, or four elements from each, looking for zeroes. The most naive search through such a table could take on the order of a trillion trials to find a counterexample, which is pretty painful, but I'm sure there are plenty of ways to optimize it. Especially if you worked from high to low, you could skip enormous chunks of the search space that would take the computation out of range.

The CDC 6600 was a pretty hardcore machine; it was Seymour Cray's first design at his Chippewa Falls skunk works, according to Wikipedia. Would definitely be interesting to know how long their solution took.

Re: Counterexample to Euler's conjecture on sums of like powers

#17

A fine example of the fact that brute force is often a powerful heuristic. I believe I recall hearing from the MIT OCW Algorithms course that they often rely on computer time doing exhaustive search (i.e. brute force) to "not disprove" some algorithm they develop before sinking too much time into developing a mathematical proof.

I find it beautiful that some things in math are so easily and convincingly disprovable that brute force is a valid approach.

Once you have the numbers, it's easily reproducible.

Re: Counterexample to Euler's conjecture on sums of like powers

#18
The submitted paper is well-written and appears to be correct, but it is far too short.

No reference is made to previous attempts to study Euler's conjecture or similar conjectures (there are surely a dozen other papers that ought to be cited in the introduction).

What led the authors to consider a computer search as opposed to any other approach? Does the method generalize?

It is indicated that the CDC 6600 was used. How was the programming done? How long time did the execution take? The instance is claimed to be "the smallest". In what norm? How can you be sure that the computer program did not skip any smaller examples?

The most serious problem with the paper, however, is that the only contribution is a purely computational statement which, though a counterexample to a conjecture, does not advance mathematical theory in any way.

Due to these shortcomings, my recommendation to the editor is to REJECT the submission.

Re: Counterexample to Euler's conjecture on sums of like powers

#19

A fine example of the fact that brute force is often a powerful heuristic. I believe I recall hearing from the MIT OCW Algorithms course that they often rely on computer time doing exhaustive search (i.e. brute force) to "not disprove" some algorithm they develop before sinking too much time into developing a mathematical proof.

I think "exhaustive search" is a misnomer here, as one obviously cannot exhaustively search the integers. (Unless we might say the machine gets exhausted.)

Re: Counterexample to Euler's conjecture on sums of like powers

#20
post #10

Earlier quoted context omitted.

No? 434437¹⁵ + 588129¹⁵ = 352114612798389918432959038931874707477944791745072116429171623348641601872653349744942 588544¹⁵ = 352114612798389919037509191076162751408804961099244071160111294752887772695040228327424 It’s apparently close enough to fool Google, but it’s not correct.

~10^-18 difference as a fraction of the latter power [0], but still a substantially huge number (on the order of 10^68) [1]. [0] https://www.wolframalpha.com/input/?i=588129%5E15+%2B+434437... [1] https://www.wolframalpha.com/input/?i=(+588129%5E15+%2B+4344...

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