4. The number of integer points within the triangle $O A B$ (where $O$ is the origin) bounded by the line $y=2 x$, the line $x=100$, and the $x$-axis is $\qquad$ .
4. 9801 The point $(x, y)$ is inside the $\triangle O A B$ if and only if $y>0, x>0$, for $x=k(1$ $\leqslant k \leqslant 99), y$ can take $1,2, \cdots, 2 k-1$, so the total number of integer points inside $\triangle O A B$ is $\sum_{k=1}^{99}(2 k-1)=99^{2}=9801$.