3. $n$ people $(n \geqslant 3)$ stand in a circle, where two specified individuals $A$ and $B$ definitely do not stand next to each other. How many such arrangements are there?

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3. $n$ people standing in a circle have $(n-1)!$ ways to stand, among which the ways to make $A, B$ adjacent are $2 \times(n-2)!$ ways, thus the ways for $A, B$ not to be adjacent are $(n-1)!-2 \times(n-2)!=(n-3)(n-2)!$ ways.