number of permutations with no three-term increasing subsequence.

Правка en1, от Yellow.Flash, 2016-10-30 09:53:19

Can someone please proof how number of permutations of first N natural numbers with no three-term increasing subsequence can be given by the Nth catalan number .. ?
More formally number of permutations such that there doesn't exist any i<j<k for which a[i]<a[j]<a[k].

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en1 Английский Yellow.Flash 2016-10-30 09:53:19 346 Initial revision (published)