An acoustic panel intended to be fixed internally to a fan casing of a turbojet engine, including an exterior face and an interior face which are curved about an axis, and two axially opposed transverse faces, the exterior curved face having at least one first recess on the side of a first transverse face and at least one second recess on the side of the opposite transverse face, said recesses each an attachment, in which said recesses do not open onto the interior curved face of the panel. Also covered are the turbojet engine including these panels and the method of mounting them.