Monster puzzle
Arto Inkala's 2012 puzzle
11.9SE grade
By The Hardest Sudoku Team · Last updated
8
3
6
7
9
2
5
7
4
5
7
1
3
1
6
8
8
5
1
9
4
The puzzle as published (21 clues). Solution not shown.
- SE grade
- 11.9
- Creator
- Arto Inkala
- Year
- 2012
Origin and lore
In 2012 Finnish mathematician Arto Inkala released a puzzle he described as the hardest he had ever made — a successor to his earlier 'AI Escargot'. International press widely reported it as 'the world's hardest Sudoku'. It has no simple-technique entry point and demands long forcing chains throughout, placing it near the very top of the SE grade scale.
Source: Arto Inkala; widely reproduced in 2012 press coverage (e.g. The Telegraph, Daily Mail).