“…The principal part of the investigated equation has mixed multiple-complicated characteristics with m, n order (m, n ≥ 1). It should be noted that for specific values of m, n, the solvability problem for second (m = 0, n = 2), third (m = 1, n = 2), fourth (m = 1, n = 3) and fifth (m = 5, n = 0)− order operator differential equations have been studied elsewhere (see [1]- [7], [16]). This study differs from the study in work [5].…”