The Risalat ul Adad is the first chapter of Ikhwan us Safa. Adad-arithmetic is the foundation of all other disciplines. The objective of arithmetic is to train the minds of learners and prepare them for philosophy.
All numbers-whole and fractions-either add up to or break down to one. Allah is One, and from Allah begins the count of all creatures. Like the number one, Allah cannot be divided into parts, nor is there anyone like unto Allah.
Each number has its own unique characteristic. Two is the first even number, 3 is the first odd number, 4 is the first square, 5 is a circular number that keeps repeating itself-for instance, multiply 5 by 5 and you get 25, multiply 25 by 25 and you get 625, multiply 625 by 625 and you get 390625. As one can see, in all the above examples the product contains the multiplied number; 5 has the unique characteristic of preserving itself and also preserving its product. The next number, 6 also preserves itself, but it does not preserve its product-for instance multiply 6 by 6 and you get 36, multiply 36 by 36 and you get 1296. The number 6 is also the first complete number. By complete it means that any number whose parts add up to the original number is known as complete number and 6 is the first of them. For example, six can by divided wholly into three parts: half, one third and one sixth resulting in 3, 2 and 1 respectively. If we add these three numbers we get the original number 6.
Imam AS says that the hokama (sages) have always given precedence to the mastery of arithmetic before taking up higher studies of natural and other sciences because arithmetic (knowledge of numbers and the skill of counting) is an ability potentially inherent in every human soul. One just has to extract it. Arithmetic does not require parallels from other disciplines. In fact, other disciplines draw examples from arithmetic.
Contemplating the various features of arithmetic leads one to the acceptance of the soul, the place where this knowledge lies and understanding of the soul ultimately leads one to the Almighty. As it is said, the one who understands his soul understands his creator.