Numbers

What these pages cover

Each page answers the same six questions about one number: its factors, the pairs that multiply to make it, its prime factorization as a tree, the divisibility rules it passes and why, its multiples, and its exact square root. Everything is computed with exact integer arithmetic, so a square root that is not whole is given as a simplified radical instead of a rounded decimal.

How to use one

Start with the rectangles: a factor pair is a rectangle you can build out of that many squares, which turns the list into something you can see instead of memorize. Then split the factor tree a different way and watch it land on the same primes every time. When you are done reading, the drill at the bottom of the page hides the answers and asks you to find the factors yourself.