I hope this doesn’t sound like a message on the other site! I found the gridfill easier than usual, with no calculator needed, but the endgame certainly called for a calculator. This gave me mixed feelings. On the one hand, it seemed to have no connection at all with crossword solving. On the other hand, it revealed an extraordinary and beautiful property shared by these sets of numbers.
So the reason for posting this message is to encourage forumites who might be deterred by numerical puzzles to give it a go. And perhaps I may be forgiven if I slip in an unasked-for caveat: don’t overlook trivial values of N.