# A tough logic problem that might interest maths/computer folks

**URL:** <https://boards.straightdope.com/t/a-tough-logic-problem-that-might-interest-maths-computer-folks/304382>\
**Category:** Factual Questions\
**Created:** [May 18, 2005, 11:28am UTC](https://boards.straightdope.com/t/a-tough-logic-problem-that-might-interest-maths-computer-folks/304382 "2005-05-18T11:28:59Z")\
**Posts on this page:** 3\
**Page:** 2

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**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\
**Post date:** [December 22, 2005, 12:22am UTC](https://boards.straightdope.com/t/a-tough-logic-problem-that-might-interest-maths-computer-folks/304382/21 "2005-12-22T00:22:50Z")

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It’s a couple of months past the usual 3-month rule, but I’m bumping this because the Xmas edition of _New Scientist_ has an article on Sudoku that’s alerted me to the fact that a paper by Felgenhauer and Jarvis had produced a definite answer: there are 6670903752021072936960 possible grids. For more details and the paper, see [here](http://www.shef.ac.uk/~pm1afj/sudoku/).  
Their method starts off in much the same fashion as my argument above, but where I had to start fudging, they resorted to a bruteforce computer search. The final answer is about 6.6 x 10[sup]21[/sup], so **InvidiousCourgette** ’s friends had a good estimate to begin with (and my upper limit was rather good after all).

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**Author:** ![ccwaterback](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@ccwaterback](https://boards.straightdope.com/u/ccwaterback)\
**Post date:** [December 22, 2005, 3:35am UTC](https://boards.straightdope.com/t/a-tough-logic-problem-that-might-interest-maths-computer-folks/304382/22 "2005-12-22T03:35:03Z")

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9! —\>  
| 8! →   
| | 7! →   
| | |  
v v v

(9!)\*\*2 X (8!)\*\*2 X (7!)\*\*2 X … X (1!)\*\*2 = big number 🙂

Does this solve the problem?

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**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\
**Post date:** [December 22, 2005, 6:23pm UTC](https://boards.straightdope.com/t/a-tough-logic-problem-that-might-interest-maths-computer-folks/304382/23 "2005-12-22T18:23:30Z")

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Nope. It’s trickier than that.

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