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Difficulty: 3 of 5 Latest: Easy count (in Just Math)
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}.

(No Solution Yet, 1 Comments) Submitted on 2014-07-29 by Ady TZIDON   
Difficulty: 5 of 5 Bonus: Words in Common 3 (in Word Problems) Rating: 3.25
What do the following words have in common?

spy, babe, tree, wavy, skate, loyal, steep, ponder

(Solution Posted, 12 Comments) Submitted on 2003-09-03 by Bryan   
Difficulty: 3 of 5Test #1 (in Numbers)
Posted on 2014-07-29 by Ady TZIDON (No Solution Yet, 2 Comments)
Difficulty: 3 of 5Date Deduction (in Logic)
Posted on 2014-07-28 by K Sengupta (No Solution Yet, 1 Comments)
Difficulty: 2 of 5Triangle Texture (in Shapes)
Posted on 2014-07-28 by K Sengupta (No Solution Yet, 2 Comments)
Difficulty: 3 of 5One of a kind (in Just Math)
Posted on 2014-07-27 by Ady TZIDON (No Solution Yet, 3 Comments)
Difficulty: 3 of 5Covering an Ellipse (in Shapes)
Posted on 2014-07-26 by K Sengupta (No Solution Yet, 0 Comments)
Difficulty: 3 of 5The decisive straw (in Probability)
Posted on 2014-07-25 by Ady TZIDON (No Solution Yet, 5 Comments)
Difficulty: 3 of 5Testy Triplet Treat II (in Just Math)
Posted on 2014-07-25 by K Sengupta (No Solution Yet, 4 Comments)
Difficulty: 4 of 5Tiling Trial (in Shapes)
Posted on 2014-07-24 by K Sengupta (No Solution Yet, 1 Comments)
Difficulty: 2 of 53 out of 7 (in Word Problems)
Posted on 2014-07-24 by Ady TZIDON (Solution Posted, 1 Comments)
Difficulty: 3 of 5Choose-Product Conclusion (in Just Math)
Posted on 2014-07-23 by K Sengupta (No Solution Yet, 1 Comments)
Difficulty: 3 of 5Last digit counts (in Numbers)
Posted on 2014-07-23 by Ady TZIDON (Solution Posted, 1 Comments)
Difficulty: 3 of 5Orange Outlook (in Just Math)
Posted on 2014-07-22 by K Sengupta (No Solution Yet, 3 Comments)
Difficulty: 3 of 5Reverse Rigor II (in Just Math)
Posted on 2014-07-22 by K Sengupta (No Solution Yet, 4 Comments)
Difficulty: 3 of 5Getting 13 (in Just Math) Rating: 4.00
Posted on 2014-07-21 by Ady TZIDON (Solution Posted, 5 Comments)

Recently Posted Solutions:
Difficulty: 3 of 5Getting 13 (in Just Math)
Submitted By Ady TZIDON. Solution posted on 2014-07-26 12:31:21
Difficulty: 3 of 5Last digit counts (in Numbers)
Submitted By Ady TZIDON. Solution posted on 2014-07-26 06:30:16
Difficulty: 1 of 5P,Sq,P (in Numbers)
Submitted By Ady TZIDON. Solution posted on 2014-07-26 06:23:39
Difficulty: 2 of 53 out of 7 (in Word Problems)
Submitted By Ady TZIDON. Solution posted on 2014-07-26 06:17:55
Difficulty: 3 of 5Unitary perfect numbers (in Just Math)
Submitted By Math Man. Solution posted on 2014-07-25 08:46:14
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