Hi Kotaro, looks like we have another case of similar interest.
I wrote about solving this puzzle about a year ago:
"Solving MoMath's A-Puzzle-A-Day by DragonFjord"
https://community.wolfram.com/groups/-/m/t/3089870
Best wishes and have fun.
Brad-san,
I'm sorry I missed your amazing post! Your implementation is significantly faster than mine. I also found the same number of solutions for 366 days: 24405.
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