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Sep 28, 2021 at 9:33 answer added qifeng618 timeline score: 0
Feb 10, 2012 at 4:02 answer added Gjergji Zaimi timeline score: 10
Feb 10, 2012 at 0:31 comment added Richard Stanley Perhaps the following remark will be useful. One can show by a generating function argument that $$ N(n,k) = \frac{1}{k!}\sum_{i=1}^k(-1)^{k-i} \binom ki\binom{ix}{n}. $$
Feb 9, 2012 at 21:02 history asked Gary Kennedy CC BY-SA 3.0