Felgenhauer and Jarvis flip this around and observe that we really only need to count Sudoku grids where the block in the top-left corner contains the numbers 1-9 in order: Any valid grid that ...

A Sudoku is a puzzle involving a 9x9 grid into ... overlayed on the two 3x3 squares on the left and right of the central ...

Fill in each block, column (vertical line) and row (horizontal line) with numbers 1-9 The same number can occur exactly ONCE per block, column and row Complete Sudoku puzzles to earn MONOPOLY ...

Each row, column, and block must only contain the digits one through nine once. Typically a Sudoku puzzle reveals a few cells in the grid, and you must use logic to work out the rest. For instance ...