The number of elements in a power set of size <= 1 is the size of the original set + 1 more element: the empty set .

Suppose $|A|=m$ . What is the size of this set:

Let's start with a specific example:

First, let's create the power set, stopping once we hit an element whose size is greater than 1:

Notice that the number of elements of size $\leq 1$ is the size of the original set + 1 more element: the empty set.

Thus: