The number of slices required to cut the cake must be 2x.
And n = 2(2x)
When n = 2: 2(20) = 21
When n = 4: 2(21) = 22
When n = 8: 2(22) = 23
When n = 16: 2(23) = 24
So, n = 2k+1, where k is an integer which is greater than or equal to 0.
Therefore, there can never be 3, 5, 6, 0r 7 equal slices, for example.