This site investigates the four-color problem:
A beautiful gallery of fractal designs are found on these sites:
A site showing some of Escher’s tessellations is interesting:
This site shows the colorful answer to Problems 24 and 25:
You will find a wealth of information on fractals on the web. It wasn’t until we had computers that we could fully appreciate this topic. We list just a few here.
This site has many links:
This site discusses the Mandelbrot set:
This a site dealing with pentominos. This site shows the all pentomino solutions (you need to click on one of the numbers to see the particular solution). It also has links to other sites.