Eisenstein Series of 3/2 Weight and Eligible Numbers of Positive Definite Ternary Forms

Abstract

A general algorithm is given for the number of representations for a positive integer n by the genus of a positive definite ternary quadratic form with form ax2 + by2 + cz2. Using this algorithm, we study several nontrivial genera of positive ternary forms with small discriminants in the paper. As a conclusion we prove that f1 = x2 + y2 + 7z2 represents all eligible numbers congruent to 2 mod 3 except 14 * 72k which was conjectured by Kaplansky in [K]. Our method is to use Eisenstein series of weight 3/2.