Please help - Radio Code

I have just changed the battery on my Micra but the radio is requesting the security-code....something that was not supplied to me when I bought the car. I have tried all of the different sites to get the code but I'm not getting any joy.

I have taken the unit out and have the following information...

Clarion - 6 CD connect system,
Serial number - CL1081580002702
Part number - 276-0034-56

Any help would be greatly appreciated