"Hamamura Nagisa no Keisan Nooto" (Hamamura Nagisa's Calculation Notes), volume 11 by Aoyagi Aito. This volume features Ruth-Aaron pairs, Sieve of Eratosthenes, Penrose triangle, Three-pass protocol, Penrose tiling, and a lot of M.C. Escher.
It was surprising to find a math topic to be named after two baseball stars, but given the existence of Ruth-Aaron pair and Japan's love for baseball, it was perhaps inevitable that this number series would make it into Hamamura Nagisa's calculation notes. It was especially amazing how the author managed to work the numeric properties into the story, as he has always done throughout the novel series. It has been a while since I read the previous volume, but this first chapter instantly restores the familiar quality.
The one unexpected topic this time is Three-pass protocol, illustrated in a puzzle that requires transporting locks and keys. It's refreshing to find cryptography related topics in this series, although the puzzle text made the algorithm sound more complicated than it is. Three-pass protocol was featured in an amusement park with Escher themes, which also incorporated Penrose tiling, following the discussion around Penrose triangle from the chapter before. Everything is tied together in the central story that ends with Nagisa's declaration to join the terrorist group.
Naturally, you wouldn't expect Nagisa to side with the terrorists, and the one of the best part about this series is that every volume consistently meet all my expectations. This has been another great volume, looking forward to more math in the future.
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