Any positive even number greater than 2.
http://wiki.answers.com/Q/What_number_will_make_a_...

Here’s a combinatorial solution that doesn’t require summing over the 12 possible sizes. Let the rectangle be axisaligned with its southwest and northeast corners at
http://www.quora.com/Mathematics/Howmanysquares...

You can build 1 rectangle with a prime number
http://www.chacha.com/question/howmanyrectangles...

All prime numbers are odd except 2. You need a minimum of 2 square tiles to make a rectangle. For p>2, you can build (p1)/2 rectangles with p square tiles. For p=2, you can build
http://answers.yahoo.com/question/index?qid=200809...
