Study No. 40b. Two pianos playing the same piece (Study No. 40a) which in itself has two melodies in a tempo ratio of e/π.
Second piano (playing slightly faster than the first) starts after about 28 seconds and both pianos finish simultaneously.
When I first came upon this 25 years ago, I found it the most exciting and outrageous thing I had ever heard. It still cheers me up like no other music can.
There are better recordings available nowadays, but I love the sound of these 1927 Ampico player pianos.