Usenet Newsgroups : rec.puzzles Hall of FameThe rec.puzzles Hall of Fame is a compilation of over 500 of the most popular puzzles that have been posted and discussed in the rec.puzzles newsgroup. In most cases a detailed solution has been provided. Many of these puzzles also appear in Braingle's own collection. 

Title: Cliff Puzzle 7: 3x3 Recursion From: cliff@watson.ibm.com If you respond to this puzzle, if possible please send me your name, address, affiliation, email address, so I can properly credit you if you provide unique information. PLEASE ALSO directly mail me a copy of your response in addition to any responding you do in the newsgroup. I will assume it is OK to describe your answer in any article or publication I may write in the future, with attribution to you, unless you state otherwise. Thanks, Cliff Pickover * * * Consider the 3x3 array below. All nine digits are used exactly once. 1 9 2 3 8 4 5 7 6 Notice that "384" is twice the number in the first row, and that "576" is three times the number in the first row. Questions: 1. Are there other ways of arranging the number to produce the same result using each digit only once and the same rules? Remember, the second row must be twice the first. The third row must be 3 times the first row. 2. Start with the number in the last row (e.g "576" or any other solution you may find) and continue to form another 3x3 matrix using the same rules with the new starting number. In other words, the number in the second row must be twice the first. The third row must be three times the first. (For this problem you may truncate any digits in the beginning. For example, 1384 would become 384.) Keep going. How many matrices can you create before it is impossible to continue. Again, each digit must be used only once in each matrix.
Solution