Creating playful games to support domain-specific learning is a complex task. This paper presents the design and development of Prime Slaughter, a computer game to play with abstract mathematical concepts, like factorization and
primality. The target group is composed of primary and early secondary school students. Following the findings of a participatory design study about children interaction in museums, our game maps operational aspects of prime
factorization onto a gameplay inspired by 2D action-adventure games, where primality and factorizaton are experienced in a visual and direct way. The museum study also suggests to support learning by multiple play styles and goal-directed
activities. A new participatory design study is about to start, to validate and improve the latest prototype of the game.