... LeVeque, Ftrndamentals of Number Theory, Addison-Wesley, 1977. H. Rademacher, Lectures on Elementary Number Theory, Krieger, 1977. K. H. Rosen, Elementary Number Theory and its Applications, ... any number divides both a and b, it must divide rl, and then, since it divides 14 I. Some Topics in Elementary Number Theory 2 Divisibility and the Euclidean algorithm 15 b and rl, ... remainders and also a and 6. Thus, it is the g.c.d., because the g.c.d. is the only number which divides both a and b and at the same time is divisible by any other number which divides a and 6....