the one thing that impresses me is, however, the starting grid for the puzzle. it consists of two squares rotated 45 degrees right in which the numbers 1-9 are placed in order, top to bottom

*then*left to right. one square is at top right, one at bottom left. preserving rotational symmetry (180 degrees about the diagonal) while removing reflectional, two numbers are also placed in the top-left and bottom right squares.

which brings me to another question - is the starting setup of a sudoku puzzle copyright? i guess it probably is, and apologies to the guardioan for the following (although it is fair use, as a quote for review purposes or a citation for educational purposes perhaps?) i also assume that the

*finishing*grid might be copyrighted/able, since it is concievable someone could solve your puzzle then produce another starting position that is derived from your finhing grid... or should i just be pleased with the guardian's hard work on the design of (at the very least) puzzle number twenty four, medium:

...|...|1.. 1

.5.|..2|.4. 5 2 4

6..|.3.|5.7 6 3 5 7

---+---+--- 6 8

...|..6|.8. 1 9

..1|...|9.. 2 4

.2.|4..|... 3 5 7 6

---+---+--- 6 8 2

3.5|.7.|..6 9

.6.|8..|.2.

..9|...|...

now, i've been trundling around the web and found some interesting sudoku related things... firstly, this is an automated web sudoku solver which also gives a list of the steps it took to find the solution. there's a blog which gives the solutions to various newspaper puzzles as well. regarding my query about the total number of sudoku grids possible, this blog thread seems to have come up with an answer - the maths is as hard as i thought it would be, and i'm sure it would have taken me a lot longet to work it out - i was still nowhere near. the number is apparently

**6,670,903,752,021,072,936,960**which is equivalent to

*9! x 72^2 x 2^7 x 27,704,267,971*. see also the wikipedia entry for sudoku for a lot of interesting information...

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