Bartosz Bialek's game Cotrio is pure math. The object is to get each of the 6 circles in the big triangle to be colored. To color one circle, it must be the sum of 2 other numbers, provided that all 3 circles form a triangle.
Each round consists of 33 moves. Each round consists of just 3 numbers. Image #4 shows an example.
Solving for the extreme circles is easiest because they are part of the Big Triangle. One rule that is important is that no two adjacent circles can have the same number.
Cotrio is a very serious, yet simple to learn, pure math puzzle. I've done only 12 levels but will certainly do more.