Using Inclusion-Exclusion, find the number of ways to write a word of length k over an n-letter alphabet so that the word uses every letter at least once?
how should I approach this?
find the number of ways to write a word of length k over an n-letter alphabet so that the word uses every letter at least once?
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combinatorics
inclusion-exclusion
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0Why don't you first search this site for similar problems ? – 2017-02-08
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0@true blue anil I couldnt find anything similar, perhaps you could give me a link? – 2017-02-08
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0This is inclusion-exclusion with Stirling numbers which was presented e.g. at this [MSE link](http://math.stackexchange.com/questions/2109526/). – 2017-02-08
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0@ Marko Riedel would you please give me some hints? I did not understand the link at all. I can not relate the method of inclusion and exclusion to the asking of this question. something is missing without which I just can't seem to understand what the question is asking. – 2017-02-12