Euler may not have cracked this problem completely, but it led to a lot of important work, including on what we today know as sudoku.

Struggling to solve today's sudoku? Is your tried and tested method hitting a brick wall and you feel like you are going around in circles? New research might make you feel a bit better: you might not necessarily be stuck... perhaps you are just in a patch of transient chaos on your way to the solution.

An algorithm for solving Sudoku puzzles from an unexpected source