This document has a list of 20 numbers that can be used to practice prime factorization. There is also a list of answers. I use these numbers during a sidewalk chalk activity with the kids. They use giant, colorful chalk to make factor trees with the numbers, and then write down their answers on the half sheet of paper. These problems are also great for board races, small white board practice, or for you to use to create your own games or worksheets.