The American Mathematical Society (AMS) offers this textbook on factorization free on its Web site. This is the third and most recent edition of the book, published in 2002. Mainly suited for graduate level math students or other university researchers, it gives the prime factors of hundreds of numbers that fall into a characteristic form. The material is presented in massive tables, and detailed instructions with examples are given that describe how to use the tables. Individual chapters are bookmarked to make it easy to navigate. The main page of AMS Books Online lists many other references free for download.