Function octave_and_number 

pub fn octave_and_number(number: i32) -> (i32, i32)

The octave and the number within it music21’s base40ToPitch reads a base-40 number as. music21 divides with a float and lets the octave setter drop the fraction, so the octave is the quotient cut toward nought, and the number within it is what is left after that many octaves.