Exercise 4.3.2 ($\mu(n) \mu(n+1) \mu(n+2) \mu(n+3) = 0$)

Proof. One integer $m$ among the four consecutive integers $n,n+1,n+2,n+3$ is divisible by $4$, so $m$ is not square free. Then $\mu (m)=0$.

If $n$ is a positive integer,

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