The present invention relates to an acoustic panel (6) intended to be fixed internally to a fan casing (1) of a turbojet engine, comprising: an exterior face (61) and an interior face (62) which are curved about an axis, and two axially opposed transverse faces, the exterior curved face (61) having at least one first recess (9) on the side of a first transverse face and at least one second recess (12) on the side of the opposite transverse face, said recesses each comprising a means of attachment, in which said recesses do not open onto the interior curved face (62) of the panel. The invention also covers the turbojet engine comprising these panels and the method of mounting them.