Re: Please, urgent!!!

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#23

From: Samuel Sené
Date: Sat, 15 May 1999 00:00

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Sorry for French people, je n'ai pas le courage de re-traduire le texte
d'anglais que j'ai d�j� eu du mal � �crire.

> I need help with this problem:

I give a hint for the beginning of the problem. (I think I'm true but there
can be an error... but I'm sure it's something like that).
Let's take s a permutation.
s(1)<>1, ok. So s(1)=j (we have (n-1) choices). if s(j)=1, that's great cause
we have P(n-2) possibilities after. But if s(j)=k, k<>j,1 (n-2 choices), we
must go again.
Let's think a little with that, we find:
P_n=(n-1)*[P_(n-2)+(n-2)*[P_(n-3)+...]]...] and that's exactly:
P_n=(n-1)(P_(n-1)+P_(n-2)).
Great! And now, I'm sure (I didn't try) that a recurrence (I don't know the
english word) works to finish the first question. And the second musn't be too
hard (a sum, I think...).
Samuel

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From: Samuel Sené <rene.sene@wanadoo.fr>
Subject: Re: Please, urgent!!!
Date: 1999/05/15
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Newsgroups: uk.education.maths,uw.math.mathsoc,fr.education.entraide.maths,york.mathstat.course.math2221,york.mathstat.course.math4100,aus.mathematics

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