180 Days of Ideas for Discussion in Math Class.
(as of 9July2014, we're in overtime!)
The pyramid has 80 cans (bottom is 6*6, 2nd layer is 5*5, 3rd layer 4*4 and top 3 cans). As for stacking it, I'd be inclined not to have a pyramid, but make a base of 5*4 cans and stack 3 more on each. The base of each cans tend to have groves for the cans to fit in.
The cans are in hexagonal dense-pack, each layer is triangular in shape. Total is not 80.
Is it 3 + 10 + 15 + 21 = 49 cans?