I started my book by the Euclidean division and these basics, the mainstay of the mathematical sciences.Know how a simple division is paramount, but the most important as it is know how to use all its features, to solve all the exercises algebra and analysis contained in the various programs of senior levels.My second chapter is devoted mainly to detail and, in the search method common divisors and not common and multiple natural numbers. This will enable you to solve simple fraction and a digital function or other origin containing fractional coefficients.My final chapter teaches you the search method of the greatest common divisor(GCD) and the least common multiple (LCM) of natural numbers.In all chapters, you can help by solved exercises in it to help you understand.