I've gotten hooked on Ken Ken. It's like Sudoku with extra constraints.
Numbers 1-9 must occur in every row and column.
Clusters of numbers must also obey rules.
Within a cluster,
- 15+ means they must sum to 15. e.g. 6 and 9.
- 5- means the (two) numbers must differ by 5. e.g. 3 and 8.
- 72x means their product must be 72, e.g. 2 4 9.
- 4/ means the (two) numbers must have 4 as a quotient. e.g. 2 and 8.
Clusters for + and x can have any number of members.
For - and / there obviously can be only two members in a cluster.
I find the "expert" 9x9 puzzles can provide 30-60 minutes of fun.
Here's one for you: