Killer Sudoku combines Sudoku with arithmetic: besides filling every row, column and box with 1-9, the dashed cages must add up to the small number in their corner — and digits cannot repeat inside a cage. On Expert there are no given digits at all: the cage sums alone are enough to solve the whole grid.
New to the variant? Read about Killer Sudoku and math variantsor warm up with classic 9x9 Sudoku.