About this 3D model

The [square pyramidal numbers](http://en.wikipedia.org/wiki/Square_pyramidal_number) are the sums of the first n squares: 1^2 + 2^2 + ... + n^2 = n (n+1)(2n+1)/6. This puzzle illustrates a nice geometric proof of this sum formula. The original sum is represented by a step pyramid where the (square) levels contain 1^2, 2^2, 3^2, ... , 5^2 blocks. The challenge is to assemble six of these pyramids into a 5 x 6 x 11 box.