Added information about unique possible sudoku combinations

sudoku.tex

@@ -266,6 +266,8 @@ It was later imitated in the 1980's by the Japanese publisher Nikoli who introdu
 
 In 1997, Wayne Gould, a retired judge from New Zealand who had moved to Hong Kong spotted the puzzles in a Japanese bookshop and then spent the next six years developing a computer program to create sudoku puzzles, and started selling them local newspapers and eventually to the London \textit{Times}. He also publishes them from his own website at \kref{https://sudoku.com/}{https://sudoku.com/}.\footnote{See \kref{https://www.theguardian.com/media/2005/may/15/pressandpublishing.usnews}{https://www.theguardian.com/media/2005/may/15/pressandpublishing.u\\snews} for more information.}
 
+There are 6,670,903,752,021,072,936,960 possible sudoku puzzles possible, but many of them are reflections or rotations of one another. When those are accounted for, there are 5,472,730,538 truly unique sudoku grids, which is a considerably smaller number, but means that you are unlikely to run out of sudoku puzzles to play.\footnote{See \kref{https://web.archive.org/web/20171112153047/http://www.afjarvis.staff.shef.ac.uk/sudoku/}{https://web.archive.org/web/20171112153047/http://www.afjarvis.sta\\ff.shef.ac.uk/sudoku/} for more information on how these numbers were calculated and information on other variants (such as 2x3 and 2x4 grids).}
+
 
 \chapter{The Rules of Sudoku}