There are 6,670,903,752,021,072,936,960 possible combinations for completing a 9-by-9 Sudoku grid, but only 5,472,730,538 of them really count for different solutions. Needlessly to say, you need a handful of lifetimes to solve all of them.
Enter numbers into the empty cells so that each row, column and 3x3 box contains the numbers 1 to 9.