A divisibility problem Erick and I worked on together was featured on the website "Open Middle".
What is an Open Middle problem? From their website:
Teachers in our province are implementing a new curriculum this school year and the first topic addressed in grade 7 is divisibility rules. Some teachers were surprised at the emphasis on this topic; the more we reflected on it, the more we realized that divisibility is a topic that builds deep number sense and operational fluency. We need to be careful not to teach "the rules" but rather the conceptual understanding and mathematical connections. This lays the groundwork for future success with a number of topics such as factoring quadratics, sequences, and polynomial long division.
Check out our submission! http://www.openmiddle.com/divisibility/