This blanket illustrates an example a perfect square dissection, the 9-square rectangle. It consists of 9 squares, all of different side lengths.

The blanket consists of 9 squares of double crochet (dc). You can choose three colours of yarn such that no two squares of the same colour share an edge! In graph theory (math lingo alert) what I mean is that the dual of the adjacency graph of the squares is 3-colourable.

To read more about the math problem I suggest the wolfram page: http://mathworld.wolfram.com/PerfectSquareDissection.html