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Dividing A Grid (Posted on 2005-10-25) Difficulty: 3 of 5
Each square of the 5x5 grid below contains a number 1-25. Divide the grid into five regions so that the number of squares and the sum of the squares in each region are both odd prime numbers. (1 is not a prime)
For example, the region consisting of {2,3,8} is a valid region. It contains 3 squares (3 is an odd prime) and the sum of the numbers in the squares is prime (2+3+8=13 is an odd prime).
+--+--+--+--+--+
| 1| 2| 3| 4| 5|
+--+--+--+--+--+
| 6| 7| 8| 9|10|
+--+--+--+--+--+
|11|12|13|14|15|
+--+--+--+--+--+
|16|17|18|19|20|
+--+--+--+--+--+
|21|22|23|24|25|
+--+--+--+--+--+

See The Solution Submitted by Brian Smith    
Rating: 2.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Hints/Tips possible subsets | Comment 1 of 9

 3  3  3  3  13


 3  3  3  5  11


 3  3  5  7  7


 3  5  5  5  7


 5  5  5  5  5


  Posted by Charlie on 2005-10-25 11:48:45
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