In a 2D the answer is two, and a 3D space can be tiled in shapes that have no corners at all, called soft cells. These shapes can be made in a few different ways, and some are shown here.

These 2D machines can shapeshift into moving 3D robots Mori3's triangular, modular design allows it to fuse with its companions, and could one day make it into space.

It is the world's first 3D-printed hotel, says El Cosmico owner Liz Lambert and the partners behind the project - Austin, Texas-based 3D printing company ICON and architects Bjarke Ingels Group.