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I know this is an extremely noob question, but I need some help. since I am stuck

Prove the formula

$$p(n,r) = \frac{(n + 1 -r) \; (r^2 - 3r + 3) \; (r-2)!}{n!}$$

from this answer.

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    "$r2-3r+3$"? Not sure what the $r2$ is supposed to mean, there.2012-06-17
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    I’m afraid that you’re going to have to provide more explanation of what you want, because I can’t make heads or tails of this. Also, is $(r2-3r+3)$ supposed to be $(r^2-3r+3)$?2012-06-17
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    @BrianM.Scott : Yes it is supposed to be (r^2−3r+3)2012-06-17
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    @CameronBuie : Please see the link, I have enclosed alongside2012-06-17
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    I’ve looked at the link, and I’m afraid that I still have no idea exactly what you’re asking. What is the connection between your question and the other question or its answers?2012-06-17
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    @BrianM.Scott : http://math.stackexchange.com/a/21273/33870 just towards the end of the answer, its written :- they are only required to sum up n−r. Actually, there are n−r+1 alternatives. Then we get the total number of permutations that give r unsorted cards, and divide over all the permutations: p(n,r)=(n+1−r)(r^2−3r+3)(r−2)!n! I just cant understand, how he wrote it ?2012-06-17
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    Okay; I’ve edited the question to make it clearer.2012-06-17
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    Thanks @BrianM.Scott : I understand, it is much clearer now :)2012-06-17
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    Why not ask this on the page itself (the author of the answer was connected to the site 8 minutes ago...)?2012-06-17

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