一个二元二次同余方程解的计数

设n是任意正整数,令Z_n是模n的剩余类环,并且Z^*_n是模n的即约剩余类环,即Z^*_n={s:1≤s≤n, gcd(s,n)=1}。通过利用同余理论与指数和的相关结果来研究集合T(a,b,c,n)={(x,y)∈(Z^*_n)²:ax²+by²+c≡0 mod n}的元素个数并给出集合T(a,b,c,n)元素个数的确切计算公式。

Counting solutions of a binary quadratic congruence equation

Let n be a positive integer. Denote by Z_n the ring of residue classes mod n, and by Z^*_n the group of units in Z_n, i.e. Z^*_n={s:1≤s≤n and gcd(s,n)=1}. The main purpose of this paper is using congruence conclusion and some results of exponential sums to study the number of elements of the set T(a,b,c,n)={(x,y)∈(Z^*_n)2:ax2+by2+c≡0 mod n} and give an exact computational formula for the number of elements of T(a,b,c,n).