If k is greater than one, F 2 − F 1 is a negative number; thus, the added inverse-cube force is attractive. Conversely, if k is less than one, F 2 − F 1 is a positive number; the added inverse-cube force is repulsive. If k is an integer such as 3, the orbit of the second particle is said to be a harmonic of the first particle's orbit; by contrast, if k is the inverse of an integer, such as 1 ⁄ 3, the second orbit is said to be a subharmonic of the first orbit.