1. Take every two distinct numbers from the set $\{1,2, \cdots, 19\}$ and multiply them. Then the sum of all such products is $\qquad$
$\begin{array}{l}-1.16815 . \\ \frac{1}{2}\left((1+2+\cdots+19)^{2}-\left(1^{2}+2^{2}+\cdots+19^{2}\right)\right) \\ =\frac{1}{2}(36100-2470)=16815 .\end{array}$