A:Answer Bern , I believe that's actually correct I don't have mine with me at this time but I have seen this in the past , when Logitech sells this keyboard without the mouse it sells as a K520, the mouse sells as a another number (I cannot remember which, M510 I think). Nothing is wrong that's just how Logitech numbers them, MK530 is a set of a K520 keyboard and a mouse. The cheaper MK520 set at at discount stores the mouse has no side buttons (M310 mouse) , the Mk530 (this set) the mouse has side buttons (M510 mouse I think), but the keyboard in both sets is the same and is numbered a K520.