Assign numbers 1 to 9 in the empty boxes so that in each 3×3 block, row and column all numbers from 1 to 9 are present without repetitions. The dotted lines indicate areas which also contain a non-repeating set of digits. These squares can be added together to produce the sums shown in the clues.
Click on the numbers in the top right part of the screen to select the number. Click on an empty box to write the number. Click on a previous written number to delete it.