  We study the asymptotic behaviour of $\sum_{m,n\le x} \tau_{1,2}(mn)$, where
$\tau_{1,2}(n) = \sum_{a b^2 = n} 1$, using multidimensional Perron formula and
complex integration method. An asymptotic formula with an error term
$O(x^{10/7})$ is obtained.
