Automatic number combination

I have Table 1 with Field IDTable1 [autonumber] [and other fields] and Table
2 with Field IDTable2 [autonumber] and Field GRV set to text [and other
Fields]
Is the following posibble:
Can I automatically generate a number that can be used in GRV field of Table
2 consisting out of a combination of IDTable1 and IDTable2 written as
IDTable1/IDTable2 in the GV field of Table 2

I want this GRV number as a unique number identifying Table 1 and Table 2

Thanks for the help