If it's a mechanical combination that was already set by the manufacturer, you should be able to give them the serial number and get the numbers, as was mentioned previously. If it's a digital like my Cannon, your Dad probably followed the instructions that came with it and changed the original numbers after he opened it and it probably has his own unique numbers now. If the latter is the case, you may be screwed and have to get a locksmith to open it. Good luck!