Make a square from each of these lists of aspect ratio $1:2$ rectangles
1, 4, 5, 6, 7, 9, 11, 12, 13, 14, 15, 17
1, 2, 3, 5, 6, 8, 11, 12, 13, 14, 17, 20
Both tilings are unique. '$1$' means $1\times2$ and '$4$' means $4\times8$ etc... No overlaps/gaps of course.
Trivial by computer, fairly tough by hand. Logic will speed you up.