CISRA Puzzle Competition 2007  SolutionsThis is the archive of the 2007 Puzzle Competition. Please visit the current competition site for information about the latest Puzzle Competition. C.3 IconoclastIntuitive Leap: For each prime number, pixels are turned on or off depending on whether each number in the grid has that prime number as a factor. The prime factors of each number are:
Using each prime factor in turn, we can make a picture by turning a pixel on in each grid position, if the number in that grid position is a multiple of that prime factor. Eight pictures can be formed this way: 2: 3: 5: 7: ++ ++ ++ ++  *   *   * *   * *   *   ***   *****   * * *   *   *****   *****   * * *   *  *******  * *   *****   **   *   * *   *   ***   * *   ***   *   *   *   *****   *  ++ ++ ++ ++ Crotchet Umbrella Rook Trident 11: 13: 17: 19: ++ ++ ++ ++  * *  ****   *****   ***   *****  *  ** **  *****  ******* * *  *** *** ** * ** ******* *** * * ******* *******  ** **  * *** * * *  * *    * *  * *** *  * *   *  * **  *****   * *  ++ ++ ++ ++ Australia Iron Nuclear Space invader The first letters spell CURTAINS, which is the answer.
