@uau: With the suggestion that Oleg's first solution was not yet optimal, you are probably right, because I received an E-mail from IBM's puzzlemaster Oded dated Nov 12, 2019, 10:22 AM, in which he reported that now the problem was solved. I guess I will not reveal any secrets or anything private now if I quote this:
Quote:
...
I'm happy to tell you that I just got, from Oleg, a solution to the open problem:
941568327
594632187
859214736
437981526
368197254
175829634
682473951
716746491
223355889
Note that it has some nice properties.
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