6. For positive integers m and n, let f(m, n) be the number of words of length n over the alphabet [m] which do not equal any of their own cyclic shifts. Use Mobis inversion to find a formula for f(m, n). (For example, 131221 is counted by f(3,6), but 133133 is not.) 6. For positive integers m and n, let f(m, n) be the number of words of length n over the alphabet [m] which do not equal any of their own cyclic shifts. Use Mobis inversion to find a formula for f(m, n). (For example, 131221 is counted by f(3,6), but 133133 is not.)