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Ìú¸Ëľ³æ (СÓÐÃûÆø)

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For n>=2,we note Pn the number of permutations ¦Ò  of  the  set {1,2,¡­,n} such that there is a single integer i¡Ê{1,2,¡­,n-1}such that  ¦Ò(i)>¦Ò(i+1).Find Pn.
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Ìú¸Ëľ³æ (СÓÐÃûÆø)

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Originally posted by gorilla at 2006-11-4 16:55:
(n-1)*n/2

4Â¥2006-11-05 13:32:57
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