<P> In this formula, if d <n, then SR (n / d) = 0, and for d = n: SR (n / d) = 1 . Therefore, SP (n) = μ (n). </P> <P> This is the special case c (1) of Ramanujan's sum c (s), defined as the sum of the sth powers of the primitive nth roots of unity: </P> <Dl> <Dd> c n (s) = ∑ a = 1 gcd (a, n) = 1 n e 2 π i a n s . (\ displaystyle c_ (n) (s) = \ sum _ (a = 1 \ atop \ gcd (a, n) = 1) ^ (n) e ^ (2 \ pi i (\ frac (a) (n)) s).) </Dd> </Dl> <Dd> c n (s) = ∑ a = 1 gcd (a, n) = 1 n e 2 π i a n s . (\ displaystyle c_ (n) (s) = \ sum _ (a = 1 \ atop \ gcd (a, n) = 1) ^ (n) e ^ (2 \ pi i (\ frac (a) (n)) s).) </Dd>

If w be the cube root of unity which of the following matrices has inverse