Korsräkner

Korsräkner, also known as cross counters, are traditional Swedish wooden puzzles that consist of a series of numbered squares arranged in a grid. The objective of the puzzle is to fill the grid with numbers from 1 to the total number of squares in such a way that the sum of the numbers in each row, column, and the two main diagonals equals the same total. This total is often referred to as the "magic constant" and is calculated as the sum of all numbers from 1 to the total number of squares divided by the number of rows (or columns).

The history of korsräkner can be traced back to the 17th century, with the earliest known examples dating from the 1630s. They were popular among Swedish schoolchildren as a means of practicing arithmetic and logical thinking. The puzzles were often carved into wooden blocks and used as educational tools in Swedish schools until the mid-20th century.

Korsräkner come in various sizes, with the most common being 3x3 and 4x4 grids. Larger sizes are also available, but they become increasingly difficult to solve. The puzzles can be solved using trial and error, logical deduction, or by using algorithms specifically designed for solving magic squares.

Today, korsräkner are primarily a historical curiosity, but they remain an interesting example of how mathematical puzzles have been used to educate and entertain people throughout history. They are also appreciated by puzzle enthusiasts for their unique challenge and the satisfaction of solving a complex problem.