Koburin is a logic puzzle published by Nikoli. A rectangular or square grid contains numbers in some cells. The aim is to blacken some cells and draw a single continuous non-intersecting loop that properly passes through all empty white cells. The number in the cell indicates the total number of black cells orthogonally adjacent to this cell. The grid may contain black cells not adjacent to cells with numbers. Cells with numbers must not be blacken. Two black cells must not be orthogonally adjacent.
Cross+A can solve puzzles from 3 x 3 to 30 x 30.