You are given a 20x20 board with some black blocking pieces.
You place your squares by clicking the top left and bottom right positions for such a square.

A squares can be adjacent to a block, but not adjacent to another square, not even diagonally.
When you have filled the board this way, the number of squares used should be as small as possible.
The right border shows the target and the square counter. You win when you have placed the required number of squares and no moves are left. If moves are left, you lose.

You can delete an existing square at any time by clicking the same position twice.

If you want to see which positions are still to be covered, hit F7 key or switch on the corresponding permanent display via the menu otpion View/Options/HighlightMovable

Variants:
There are 27 fixed setups and 4 variants with random setups.
These targets have been found by hand; so you might be able to improve on them.

Please note that there are several alternative piece sets.

This game was inspired by a mathematical problem stated in 2005 at the PQRST puzzle competition (http://www.otuzoyun.com/pqrst).

Related games: 'Area', 'Area For Two', 'Square Down', 'Square The Square', 'Square The Square II'.