Prime numbers are a consequence of the multiplication operation between natural numbers. Faced with the need to count large quantities of elements (people, animals, things) it was understood that by arranging them in rows, each containing the same number of elements, it would be enough to perform an operation, later called multiplication, between the number of files and the number of elements in each row. This solution, however, meant that for some quantities of elements it was not possible to find an exact organization of files: however you chose the number of rows and elements for each row, there were always elements. Probably some took the trouble to multiply the natural numbers from 2 to a certain n and realized that among the results of the products some numbers were skipped. Thus was born the concept of factoring. This investigation examines natural numbers, greater than 1, as a function of their ordered sequence and a second intrinsic parameter of the number itself. For this second parameter the definition of k-almost prime number is used. The investigation reveals: