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

Home > Just Math
Easy count (Posted on 2014-07-29) Difficulty: 3 of 5
Let S be a set of some positive integers.
We'll call S autonomous if the number of elements in S is itself an element of S. e.g. the set {2,3,5} is autonomous, as is the set {2,7}, but the sets {1, 4} or {2,4,5} are not.

Determine a general formula for the number
of autonomous subsets of {1, 2, 3, ... , n}.

See The Solution Submitted by Ady TZIDON    
No Rating

Comments: ( Back to comment list | You must be logged in to post comments.)
Hints/Tips re: computer assisted solution | Comment 2 of 5 |
(In reply to computer assisted solution by Charlie)

Please read the question one more time, find few samples e.g.

f(0) undefined , f(1)=1  etc and then deduce and explain the formula.

The computer is totally unneeded - you have just misunderstood the text, once you get it cleared it is a d1 or d2 puzzle.


  Posted by Ady TZIDON on 2014-07-29 23:53:21
Please log in:
Login:
Password:
Remember me:
Sign up! | Forgot password


Search:
Search body:
Forums (0)
Newest Problems
Random Problem
FAQ | About This Site
Site Statistics
New Comments (4)
Unsolved Problems
Top Rated Problems
This month's top
Most Commented On

Chatterbox:
Copyright © 2002 - 2017 by Animus Pactum Consulting. All rights reserved. Privacy Information