Henry, If you search under "sudoku" in the OEIS, you will find two relevant entries, as follows. Regards, Neil %I A109741 %S A109741 1,1,2,5472730538 %N A109741 Number of inequivalent (completed) n^2 X n^2 sudokus (or Sudokus). %C A109741 See A107739 for definition of a sudoku. %C A109741 a(2) = 2 independently computed by Gary McGuire and Hugo van der Sanden. %C A109741 For the 9 X 9 case the allowed equivalences are: relabeling entries; reflection; rotation; %C A109741 permutation of blocks of columns 1-3, 4-6 and 7-9; %C A109741 permutation of blocks of rows 1-3, 4-6 and 7-9; %C A109741 permutation of columns 1-3; permutation of rows 1-3; %C A109741 permutation of columns 4-6; permutation of rows 4-6; %C A109741 permutation of columns 7-9; permutation of rows 7-9. %D A109741 J.-P. Delahaye, "Le tsunami du Sudoku" in 'Pour La Science' (French Edition of "Scientific American"), December 2005 pp 144-9, Paris. %H A109741 Bertram Felgenhauer and Frazer Jarvis, <a href="http://www.shef.ac.uk/~pm1afj/sudoku/">There are 6670903752021072936960 Sudoku grids</a> %H A109741 J. P. Grossman, <a href="http://www.mathstat.dal.ca/~jpg/sudoku/">Javascript Sudoku solver</a> %H A109741 Ed Russell and Frazer Jarvis, <a href="http://www.shef.ac.uk/~pm1afj/sudoku/sudgroup.html">There are 5472730538 essentially different Sudoku grids</a> %H A109741 Wikipedia, <a href="http://en.wikipedia.org/wiki/Sudoku">Sudoku</a> %H A109741 S. Gupta, <a href="http://theory.tifr.res.in/~sgupta/sudoku/challenges.html#prime">Exploring the Mathematics of Su Doku</a> %e A109741 a(2) = 2: %e A109741 12|34 12|34 %e A109741 34|12 34|12 %e A109741 --+-- --+-- %e A109741 21|43 23|41 %e A109741 43|21 41|23 %K A109741 nonn %O A109741 0,3 %A A109741 njas, Aug 13 2005 %I A107739 %S A107739 1,1,288,6670903752021072936960 %N A107739 Number of (completed) sudokus (or Sudokus) of size n^2 X n^2. %C A107739 An n^2 X n^2 sudoku is an n^2 X n^2 array which is subdivided into n^2 n X n subarrays. Each row and column of the full array must contain each of the numbers 1 ... n exactly once (this makes it a Latin square of order n). In addition, each of the n^2 n X n subarrays must also contain each of the numbers 1 ... n exactly once. %H A107739 Bertram Felgenhauer and Frazer Jarvis, <a href="http://www.shef.ac.uk/~pm1afj/sudoku/">There are 6670903752021072936960 Sudoku grids</a> %H A107739 J. P. Grossman, <a href="http://www.mathstat.dal.ca/~jpg/sudoku/">Javascript Sudoku solver</a> %H A107739 Ed Pegg Jr, <a href="http://www.maa.org/editorial/mathgames/mathgames_09_05_05.html">Sudoku variations</a> %H A107739 Ed Russell and Frazer Jarvis, <a href="http://www.shef.ac.uk/~pm1afj/sudoku/sudgroup.html">There are 5472730538 essentially different Sudoku grids</a> %H A107739 Wikipedia, <a href="http://en.wikipedia.org/wiki/Sudoku">Sudoku</a> %e A107739 Comment from Hugo van der Sanden (hv(AT)crypt.org), Jun 12 2005: "Consider n=2: renumbering doesn't affect the result, so we can fix row A at (1, 2, 3, 4) and multiply the result by 4!. Once rows B and C are chosen, there is only one option for row D. Row B must have (3, 4) or (4, 3) followed by (1, 2) or (2, 1). %e A107739 "Rows C and D can be swapped without affecting validity, so we can fix column 1 of row C to be the lower of the two options and multiply the results by 2. %e A107739 "That leaves at most 4 options for row C (2 choices in each of the remaining 3 positions, of which one must have our selected number as one of the choices); that leaves 16 options to check for rows B and C, the result to be multiplied by 48. %e A107739 "Checking, we find just 6 of the 16 grids are valid: %e A107739 1234/3412/2143/4321 1234/3412/2341/4123 1234/3421/2143/4312 %e A107739 1234/4312/2143/3421 1234/4321/2143/3412 1234/4321/2413/3142 %e A107739 so a(2) = 6 * 48 = 288." %e A107739 An example of a sudoku of size 9 X 9: %e A107739 124|567|893 %e A107739 378|294|516 %e A107739 659|831|742 %e A107739 ---+---+--- %e A107739 987|123|465 %e A107739 231|456|978 %e A107739 546|789|321 %e A107739 ---+---+--- %e A107739 863|972|154 %e A107739 495|618|237 %e A107739 712|345|689 %Y A107739 Cf. A109741. %K A107739 nonn,bref %O A107739 0,3 %A A107739 Richard McNair (rmcnair(AT)ntlworld.com), Jun 11 2005 %E A107739 Entry revised by njas, Aug 12 2005