To keep the spectators out of the line of flight at an air show, the ushers arranged the show's seats in the shape of an inverted triangle. Kevin, who loves airplanes, arrived very early and was seated in the front row, which contained one seat. The second row contained three seats, and those filled very quickly. The third row contained five seats, which were given to the next people who came. The next row contained seven seats. This seating pattern continued all the way to the last row, with each row containing two more seats than the preview row. All 20 rows were filled. How many people attended the air show