It is obvious that this afgan/wall-hanging has the seven colours of the rainbow and that it has squares but it also repesents one way of generating square numbers.

Every square number is the sum of odd numbers. The odd numbers here are shown in the L shapes:

1 + 3 + 5 + 7 + 9 + 11 + 13 = 49, which is the square of 7.

This is a very easy design to make, worked entirely in garter stitch. It doesn’t have to be worked in rainbow colours. I think it would be very effective with alternating bands of black and white.

Read the story of this afghan on Ravelry or on Woolly Thoughts web site.