When musical notes sound good together, “our ears are doing math.”
This fantastic explainer on the harmonic series , in typical Andrew Huang fashion, requires no prior musical (or even mathematical) knowledge, yet quickly escalates into territory as “mind-blowing” as it is fundamental to, well, nature itself and the human experience:
Try It Yourself
The interactive harmonic diagram, which Andrew uses to demonstrate the harmonic series, is available to play (via Alexander Chen on GitHub):

Further viewing
Here is the explainer from Smarter Every Day which Andrew references, ‘What is a Fourier Series? (Explained by drawing circles)’: