The number of permutations with k fixed points

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Could someone help me please with this problem? I don't even know how to start it.

For 1$\leq$k$\leq$n, find the number of permutations $\theta$ $\in$ $S_n$ that have exactly k fixed points.

Thank you in advance!

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For the case $k=0$, this is the problem of derangements.

For $k > 1$, after first choosing $k$ members of $\{1,\ldots,n\}$ to be the fixed points, you then want a derangement of the remaining $n-k$.