Problem of the Week 1014

Dominating Bishops

How many ways are there to place 9 bishops on a 9x9 chessboard so that they dominate the board, meaning that every square is attacked by a bishop (or has a bishop on it)?

Source: A nice new book containing many chessboard puzzles by John Watkins, Across the Board, Princeton University Press, Problem 7.4.

© Copyright 2004 Stan Wagon. Reproduced with permission.