[seqfan] Re: Xmas-challenge

[Rob Pratt]

I had forgotten that I worked on this in 1998.  This time I used the integer linear programming solver in SAS to solve an optimal subtour problem. I’ll update the entry with more detail.

> On Dec 28, 2020, at 7:59 AM, Peter Luschny <peter.luschny at gmail.com> wrote:
> 
> Rob Pratt>
> 
>> 76 is optimal.
> 
> 
> Georg Fischer drew my attention to an old (1998) internet
> discussion led by Erich Friedman [1]. There you can read:
> 
> "Robert Pratt gave the best values for n <= 16. He proved
> the values of S(n) for n <= 13 by exhaustive search. He
> formulated the problem as a graph theory problem and looked
> for long paths in the "divisor graph" using some Mathematica
> programs he wrote for this purpose."
> 
> This morning, the following happened: Robert sent in the first
> 200 terms of the sequence! [2] Our discussion was worth it
> for this treasure alone.
> 
> Chapeau! Robert, how did you calculate that? Exhaustive
> search? SAT solver? Did you use heuristics? I hope you are
> going to publish your program.
> 
> [1] https://erich-friedman.github.io/mathmagic/1198.html
> [2] https://oeis.org/A337125
> 
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