This is the most addictive game I've played in months! Literally!SquareLogic
mixes the famous magic squares with some basic arithmetic rules, (equalities, additions, substractions, divisions), but also trickier combinatorial notions that require some logic (Straights, "Greater/Less than" sequences, Odd/Even numbers...) and some littles surprises I won't spoil...
However, don't be afraid! The game was designed to focus on logic more than mathematical skills; thus, all the possible answers are given, and automatically updated to avoid headaches to the novice. (This can be toggled off for a greater challenge and a "newspapergames-ish" feeling.) For not being a mathematics lover myself, I can guarantee this game is a lot of fun!
With 6 uniquely-themed locations, each of them containing half a dozen of regions, which themselves separately contain approximately ~800 puzzles, it's not less than 20000 puzzles SquareLogic offers, promising hundreds and hundreds of hours if you wish to decipher them all! The difficulty is progressive as the grids become bigger, and each region has its own variations that make them more enjoyable.
Probably one of the best time killers you can find, if you're into logic-based number placement puzzle games, with an almost-endless replay value.