Here's a great graphic organizer to help students factor numbers 1 - 100. These can be used to teach prime/composite, odd/even, divisibility rules, skip counting, compatible numbers, factors, multiplies, GCF, simplifying fractions, and more. Link to free download included.
Math Manipulatives - Find the prime factorization of numbers by completing factor trees. Then use a venn diagram to sort the prime factors. Multiply numbers in the intersection to find the greatest common factor. Multiply all of the numbers in the venn diagram to find the least common multiple.