In Part 3, we figured out all the 7-note scales drawn from the usual 12-tone scale and obeying an extra constraint: there’s at most a whole tone between consecutive notes. We got a total of 21. They come in 3 groups of 7:
This is a companion discussion topic for the original entry at https://johncarlosbaez.wordpress.com/2023/06/19/modes-part-4/