What is the least number of white knights that can be placed on a standard chessboard so that a black piece cannot be added to an unoccupied square without being under attack?

A bit embarrassed to post this, as I'm sure there is a much better solution, but have to start somewhere:

Here's a configuration with 20 knights:

. . . . . . . .
. . x x x x . .
. x . . . . x .
. x x . . x x .

. x x . . x x .

. x . . . . x .

. . x x x x . .
. . . . . . . .

Posted by David Shin on 2005-01-26 19:46:38