4

4 is the natural whole number succeeding 3 and coming prior to 5. It is also a square number (i.e. 22) and the the fourth tribonacci number. A four sided polygon is called a tetragon while the only four sided polyhedron is the tetrahedron, one of the three-dimensional Platonic solids. This number can also be shown in Fast growing Hierarchy as ƒ1(2), and as ƒ0(3).