With these 6 pieces, you can build an n·(n+1)·(n+2) solid brick.

The volume of each piece is the sum of the first n triangular numbers.

Therefore, the sum of the first n triangular numbers is:

Σₙ Tₙ = n·(n+1)·(n+2)/6

In the provided STL file, n=6, but you could use the parametric OpenScad file to get any other value.