[seqfan] Re: Xmas-challenge

[Peter Luschny]

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