Question 17
There are 165 unit cubes arranged in 5 square layers with no space between the cubes as shown. The layers are 1 by 1, 3 by 3, 5 by 5, 7 by 7, and 9 by 9. How many unit cubes are completely surrounded by six other unit cubes? (This means that each face is shared with a face of another cube.)
