What do the numbers in set theory refer to?
A4: Each pc (pitch class) in the twelve-tone system is assigned a number. C=0, C#=1, D=2, D#=3, E=4, ….. A#=10, B=11. [If we use hexadecimal numbers the last two (10,11) are represented by A and B, allowing single-digit primes.] Numbers are also used to represent intervals in semitones. A minor third, for example, is 3 semitones, or just 3. A perfect fifth is 7, etc.
