f of seven. So what's the relationship over here? Let's see, it looks like if you multiply by two and subtract one, so two times one minus one is one, two times two minus one is three. Two times three minus five, two times three minus one is five. Two times four minus one is seven. So this is two n minus one. So the area of each of these rectangles, the base is two, and the height is f of two n minus, f of two n minus one.