Application of Eichler's reduction formula to the representation of numbers by certain quaternary quadratic forms

It is shown how Eichler's formula can be used to obtain exact formulas for the number of representations of positive integers by certain positive-definite quadratic forms of principal type in four variables, in terms of traces of Frobenius endomorphisms of appropriate elliptic curves over fields of finite characteristic; as examples, some new exact formulas are derived.