What is the number of vertices (corners) for the following cubes?

1-cube(line)
2-cube(square)
3-cube(box)
4-cube(hypercube)

A 1-cube has 2 vertices.  A 2-cube has 4 vertices. 
A 3-cube has 8 vertices, and a 4-cube has 16.

Note that for an integer n, an n-cube has 2^n (2 to the nth power) vertices.