3. Arrange the positive rational numbers in the following sequence,
$$
\begin{array}{l}
\frac{1}{1}, \frac{2}{1}, \frac{1}{2}, \frac{3}{1}, \frac{2}{2}, \frac{1}{3}, \frac{4}{1}, \frac{3}{2}, \\
\frac{2}{3}, \frac{1}{4}, \cdots,
\end{array}
$$

Then the position number of the number $\frac{1989}{1949}$ is $\qquad$
3. The number's position in the original

sequence is $(1+2+\cdots+3937)+$ $1949=7753902$,