I've spent some time considering whether it might be possible to solve the Onitiu problem of constructing a knight tour with the square numbers in a knight chain but showing birotary symmetry (i.e. unchanged by 90 degree rotation) which is possible on boards of oddly even side (10, 14,18, 22, 26, etc). So far without success, though I can see no simple argument to prove such a tour impossible.

Here is an Emperor (Knight + Wazir) tour that shows the general idea.

The red line indicates the square numbers. The other colours show its rotations. The black dots in the middle are the positions of 25, 50, 75 and 100 in this tour. It starts with 1 at d5.

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Earlier today I had my second vaccination dose against the coronavirus.