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How many ways can $N$ labelled balls be placed in $M$ unlabelled boxes, provided each box must have at least $P$ balls inside?

Naturally $N > M \times P$.

Any closed form solutions would be great!

The motivation behind this question is that I want to brute force sample each of the possible configurations for particular values of $N$, $M$ and $P$. However, given that the quantity may be fairly large I want to check how many there are before trying!

Thanks,

Ed

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For $P=1$ the answer is given by the Stirling numbers of the second kind.

For general $P$, you have the $P-$associated Stirling numbers of the second kind

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