I feel that the solution may be converting the prefecture name to Latin script too early in the process. The sixth Japanese prefecture is written in Japanese with the Unicode code points U+5C71 U+5F62 U+770C (U+770C just means, more or less, "prefecture" and isn't especially important). A solver might wish to proceed on a character-by-character basis. Checking the Unihan Database on the https://unicode.org/charts/unihan.html website gives the following results for the kJapaneseKun property:

  U+5C71 = YAMA
  U+5F62 = KATACHI KATA ARAWARERU

So, I feel that the "list item" column could be updated to:

  YAMAGA(T)A (or
  YAMA KA(T)ACHI
  KATA ARAWARERU)

The specific URL on mitmh2022.com might not work as intended in all web browsers. To reach the puzzle in question, you may have to click on this link once, press the Public Access button on the resulting page, and then click on the same link a second time. Ultimately the https://www.bookspace.world/puzzle/lists-of-large-integers/s... URL will be shown.