In 1979, Philip Glass composed some music for Sesame Street; the music was used to back geometric animations showing how a simple circle could be subdivided and repeated to make more complex shapes and patterns (in much the same way that Glass's music uses patterns, repetition, and subtle alteration to create melody and complexity). It's hard to find the resulting work (entitled "Geometry of Circles") that was shown on Sesame Street three decades ago, though it has been re-aired a few times over the years and some folks have recorded and posted snippets of the recordings to YouTube. Below, check out some of the Sesame Street/Philip Glass animations...and prepare to have your brain circles. And Philip Glass music.

And here's a short segment from the official Sesame Street YouTube channel:

Further reading: Geometry of Circles on Muppet Wiki (yes, there's a Muppet Wiki and this is not the first time I've linked to it...), Philip Glass on Wikipedia, and Sesame Street: 40 Years of Sunny Days (a DVD set which includes one of the animation clips). You've gotta hand it to these Muppet Wiki folks: they're archivists of our childhood.