[tex]\displaystyle \frac{1}{1\times 2}+\frac{1}{2\times 3}+...+\frac{1}{1565\times 1566}=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{1565}-\frac{1}{1566}= \\ \\ 1-\frac{1}{1566}= \\ \\ \frac{1565}{1566} \\ \\ Raspuns:\boxed{1565}[/tex]