Printable killer sudoku

How killer sudoku works

A killer sudoku is a 9x9 sudoku with arithmetic on top. Rows, columns and 3x3 boxes each hold the digits 1 to 9 once, as usual. The grid is also cut into cages, drawn with dashed lines. The small number in the corner of a cage is the total of its squares, and a digit cannot repeat inside a cage. So a cage of two squares marked 3 holds 1 and 2, and a cage of three marked 24 holds 7, 8 and 9. A large digit standing alone in a square is a given, as in a normal sudoku.

What is the rule of 45 in killer sudoku?

Every row, column and 3x3 box holds the digits 1 to 9 once, so each adds up to 45. Add the totals of the cages that lie completely inside one of them and take the result from 45: what is left is the total of the squares not yet counted. If only one square remains, that is its digit.

Three levels, measured on every board

Before a board goes on the page it is solved by program in three ways. The first knows cage totals, meaning which digits can make a total and every way of seating them, plus ordinary sudoku singles. The second adds the rule of 45 over rows, columns, boxes and bands of up to four neighbouring rows or columns. The third also writes candidates down and uses locked candidates and naked pairs. Easy, medium and hard on this page are those three levels. The one printed under the title is the lowest that finishes the board, the levels below it are confirmed to get stuck, and a separate search checks that the board has exactly one solution.

Cages and given digits

The standard sheets print the board 180 mm wide, 20 mm a square, which leaves room for candidates next to the cage total. The six boards in the easy group have cages of 2 or 3 squares and 11 to 14 given digits. The six in the medium group have cages of up to 4 squares and 4 to 6 given digits. The hard boards, the small cage boards and the no givens boards start with no digit at all: 16 of the 36 sheets are cages and nothing else.

The sum table and the answer under the fold

Four sheets print the board at 18 mm a square and, under it, the 12 sums that can be made in only one way: 3, 4, 16 and 17 in two squares, 6, 7, 23 and 24 in three, and 10, 11, 29 and 30 in four. Those are the cages to look for first. Four more sheets carry a small solved board at the foot of the page, under a dotted line you fold back before you start, so there is one page to print. Every other PDF has the full size solution as its second page.

Printing

Print at 100 percent or actual size on A4; black and white is enough. The cage lines are dashed and sit a little inside each square, so they stay clear of the grid lines. Use a pencil and write small: the hard boards are chosen because they need written candidates.

For sudoku without sums, start from the printable sudoku page or go up to extreme sudoku graded by technique. For sums without the sudoku rules, there is printable kakuro.