For some reason this video ended up in my Youtube recommendations last week, and I clicked on it because the thumbnail caught my attention. Didn't regret it, an

For some reason this video ended up in my Youtube recommendations last week, and I clicked on it because the thumbnail caught my attention. Didn't regret it, and I've watched a few others. Another that was pretty interesting in the development of techniques to approach it: https://youtu.be/Zk4qNEDXFSw https://youtu.be/Zk4qNEDXFSw Edit: Ah no, the first I saw was actually https://youtu.be/hAyZ9K2EBF0 https://youtu.be/hAyZ9K2EBF0 which has a diagonal rule, and a magic square in the middle.