"There aren't any Platonic solids with 7 sides never mind cubes with 7 sides. (The Platonic solids are the regular solids - there are 5 of them the cube is one and the octahedron, its dual, is another, the dodecahedron is one and the icosahedron, its dual, is another and the last is the tetrahedron, which is its own dual. The Megaminx is a dodecahedron, the pyraminx is a tetrahedron and the cube is a cube.)"
There are lots of very smart mathematician types in the speedcubing group so I'm not surprised I got an answer to the 7-sided puzzle comment. The answer makes sense of course and I now feel a bit silly for not having realised it when I made the initial comment!