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### Mostowski Collapse

Sep 19, 2022, 5:51:16 PM9/19/22
to
Rumors are, that finding an integer solution
took a lot of computing resources:

x^3 + y^3 + 42 = z^3

Can we nevertheless solve this on a PC in
less than 5 minutes?

### Nasser M. Abbasi

Sep 19, 2022, 10:24:19 PM9/19/22
to
Did you mean

x^3 + y^3 + z^3 = 42?

Given that it says at
<https://interestingengineering.com/science/the-sum-of-three-cubes-problem-for-42-has-just-been-solved>

"Charity Engine uses a computer's idle processing power, and it took 1 million
hours of processing time to solve the Diophantine Equation where
k is equal to 42. The answer is:
(-80538738812075974)^3 + (80435758145817515)^3 + (12602123297335631)^3 = 42."

I do not see how this can be found in 5 minutes on a PC? No matter
how fast the PC is. They seem to have done brute force search to find this.
But may be they used improved search method as given in

<https://news.mit.edu/2021/solution-3-sum-cubes-puzzle-0311>
under "A solution’s twist" section. But even that will stil require
very large brute search method.

But I tried

eq=x^3+y^3+42==z^3
FindInstance[eq&&Element[{x,y,z},Integers],{x,y,z},1]

And it said

FindInstance::nsmet: The methods available to FindInstance are insufficient to
find the requested instances or prove they do not exist.

in 0.001 seconds. I guess Mathematica still does not know about
the method used to solve for 42.

--Nasser

### Mostowski Collapse

Sep 20, 2022, 3:37:53 AM9/20/22
to
Well I mean:

x^3 + y^3 + 42 = z^3

You only need to consider positive x,y,z then.
Assume there is some ingenious approach to
speed it up, maybe could then also solve:

114, 390, 627, 633, 732, 921, 975.