Put minimal number of Queens on M x N chessboard to hit all the sells.

Click on "ADD...row/column" for larger boards.

There is a simple algorithm for solving the KnightMare problem on

"3 x 3" with 1 Queen, "11 x 11" with 5 Queens, '27 x 27" with 13 Queens,

as well as for square boards with side "8 x any square number +3" in general

See my article in Russian "Quant" magazine.