A new seven – story apartment building is opening in our town. I was curious when I read the apartments on the higher floors were more expensive, so I went to the open house. I discovered that there is only one very large apartment on the top floor. Each floor has twice as many apartments as the floor above it. The lowest floor contains only one-room studio apartments which are very small.

How many apartments are in this new building?

Find the generalized formula that would tell me how many apartments would be in this building if it had “X” stories?