Calcudoku Plus Puzzle Books - 400 Easy to Master Puzzles 5x5 (Volume 1)

Calcudoku (also known as "Mathdoku") is a mathematical and logical puzzle loosely similar to Sudoku.

The objective is to fill the grid in with the digits 1 through N (where N is the number of rows or columns in the grid) such that:

- Each row contains exactly one of each digit.

- Each column contains exactly one of each digit.

- Each bold-outlined group of cells (block) contains digits which achieve the specified result using the specified mathematical operation: addition (+).

- Unlike Killer Sudoku, digits may repeat within a block.