You are given a 15x15 grid and asked to cover it with rectangles whose dimensions are a power of 2. For example you can use rectangles 8x1 and 4x4, but not 2x3. The rectangles must cover every cell of the grid, cannot overlap or be outside the grid. What is the least number of rectangles needed to achieve this covering? Good luck!
This puzzle came from Mathematics Stack Exchange. Note this link contains the answer.