On higher-order differential operators with a regular singularity

A boundary-value problem for the non-self-adjoint differential operators
$$ \ell y\equiv y^{(n)}+\sum_{j=0}^{n-2}\biggl(\frac{\nu_j}{x^{n-j}}+q_j(x)\biggr)y^{(j)}, \qquad 0<x<T, $$
with a regular singularity at zero is investigated. Theorems are obtained on completeness, on the expansion with respect to the eigen- and associated functions of the boundary-value problem on a finite interval, and on equiconvergence. In addition, the inverse problem is investigated.