You might see this as just an interesting design. It is also a crochet representation of square numbers and triangular numbers.

It consists of 225 circles; 105 have dark centres, the others are plain.

Triangular numbers are what you get when you add conscecutive numbers. The circles with dark centres are

1 + 2 + 3 + 4 ……. +14 = 105

The circles without dark centres are

1 + 2 + 3 + 4 ……. +15 = 120

Add two consecutive triangular numbers and you get a square number

105 + 120 = 225, which is the square of 15

I love the idea of using circles to represent squares and triangles!

Circles will not join together sufficiently well to support their own weight, so these are attached to a backing. The circles are worked first and joined to the backing as it is made. This involves a lot of work as it is like making two afghans. The up-side is that it makes a very warm, double thickness afghan and, as can be seen from the photo of the back , it looks completely different on the two sides and is very effective when hung as a room divider.