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 Permutations count (Posted on 2015-10-01)
Find the number of permutations of (1,2,3...n) possessing the following feature:

The number n is the only local maximum e.g. 123465, 123564, 654321,
as opposed to 651432, 261354.

 Submitted by Ady TZIDON Rating: 3.0000 (1 votes) Solution: (Hide) Let f(n)=k. To evaluate f(n) note that for each one of k permutations you can get two new ones by inserting the number n+1 before or after n. So f(n+1)=2*k. f(1)=1 implies f(n) =2^(n-1)

 Subject Author Date re: error in Ady TZIDON 2015-10-02 21:29:54 error in "official solution" Steve Herman 2015-10-02 19:02:32 My misleading subject line. Jer 2015-10-02 13:38:33 one general remark Ady TZIDON 2015-10-02 13:16:01 re(2): I guess simplicity is in the mind of the user Ady TZIDON 2015-10-02 12:57:26 re: I guess simplicity is in the mind of the user Steve Herman 2015-10-02 12:10:50 I guess simplicity is in the mind of the user Charlie 2015-10-02 09:57:08 Simpler solution Jer 2015-10-02 07:28:14 re: solution Ady TZIDON 2015-10-02 00:00:20 solution Charlie 2015-10-01 16:02:09

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