  The inverse geodesic length of a graph $G$ is the sum of the inverse of the
distances between all pairs of distinct vertices of $G$. In some domains it is
known as the Harary index or the global efficiency of the graph. We show that,
if $G$ is planar and has $n$ vertices, then the inverse geodesic length of $G$
can be computed in roughly $O(n^{9/5})$ time. We also show that, if $G$ has $n$
vertices and treewidth at most $k$, then the inverse geodesic length of $G$ can
be computed in $O(n \log^{O(k)}n)$ time. In both cases we use techniques
developed for computing the sum of the distances, which does not have "inverse"
component, together with batched evaluations of rational functions.
