6. Find the integer solutions of the indeterminate equation $x^{2}+18 y^{2}=1987$.

 untranslated text:
将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。 

 translation:
Find the integer solutions of the indeterminate equation $x^{2}+18 y^{2}=1987$.

Note: The note at the end is not part of the original text and is provided for clarity.
答: $\left\{\begin{array}{l}x=23, \\ y=9\end{array}\right.$

Answer: $\left\{\begin{array}{l}x=23, \\ y=9\end{array}\right.$