Another interesting math thing I discovered years ago while designing launch systems. We were looking at clustered tanks, like a Saturn I or an Otrag vehicle, to see what the tradeoff of a cluster of small tanks was over a single large tank of the same diameter. The large tank was thicker than the smaller tanks for the same pressure, but there was more surface area with the small tanks. I was surprised to find that mathematically, the weight of metal was exactly the same. Many small tanks clustered together to get the same volume as one large tank bought you nothing. Of course, there were many other factors than math involved, like support structures, plumbing, and the easy availability of small diameter tube and pipe that make the tradeoff much more complex, but it was still kind of neat.