7
2
1
4
2
6
3
1
5
6
4
8
7
2
5
3
4
7
2
6
5
6
4
1
3
7
2
7
5
7
1
4
3
9
Finnish mathematician Arto Inkala created what is widely considered the world's hardest Sudoku in 2012.
Finnish mathematician Arto Inkala created what is widely considered the world's hardest Sudoku in 2012.
Finnish mathematician Arto Inkala created what is widely considered the world's hardest Sudoku in 2012.
Finnish mathematician Arto Inkala created what is widely considered the world's hardest Sudoku in 2012.