Concat a date and numeric field

Hello all and Happy Holidays.

I am trying to ( I think) concat two fields.

The requirement is that the Invoice field will = the UserID followed by the date.

So if User ID = 1234 and the date is 12/23/13, the Invoice Number should be 1234122313.

I've tried various things and I'm not having luck.  I'm not a programmer, so have been trying to use the built in functions of FormCalc.

Any guidance would be valuable and appreciated.

I am on Version 10.0.2.20120224 blah blah blah

Also the Date field is being done by

$.rawValue = num2date(date(), DateFmt(1))

Gretchen Sheridan