Flex made adding controls to web content easy. So I did this mathematical illustration. You can drag the red “x” and fiddle with the number.

When I originally posted it, probably 2008 or so, I said, “Until I put up an explanation, I’m sorry to say that it is likely to be something of a riddle.” Well, here it is 2020 and I still haven’t put up the explanation.

Until I do, I will give the hint that it connects Euler’s formula to the compound-interest formula for the exponential (see characterizastion #1 here).