All about flooble | fun stuff | Get a free chatterbox | Free JavaScript | Avatars    
perplexus dot info

Home > Numbers
Permutations count (Posted on 2015-10-01) Difficulty: 3 of 5
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)

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Hints/Tipsre: error in Ady TZIDON2015-10-02 21:29:54
error in "official solution"Steve Herman2015-10-02 19:02:32
My misleading subject line.Jer2015-10-02 13:38:33
Some Thoughtsone general remarkAdy TZIDON2015-10-02 13:16:01
Some Thoughtsre(2): I guess simplicity is in the mind of the userAdy TZIDON2015-10-02 12:57:26
re: I guess simplicity is in the mind of the userSteve Herman2015-10-02 12:10:50
I guess simplicity is in the mind of the userCharlie2015-10-02 09:57:08
SolutionSimpler solutionJer2015-10-02 07:28:14
Hints/Tipsre: solutionAdy TZIDON2015-10-02 00:00:20
SolutionsolutionCharlie2015-10-01 16:02:09
Please log in:
Remember me:
Sign up! | Forgot password

Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (6)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Copyright © 2002 - 2019 by Animus Pactum Consulting. All rights reserved. Privacy Information