If you are starting this database from scratch, set your Primary Key (type number) to a serial number (on creation) starting at 159 000 (or whatever starting number you need). From then on each new serial number will have that space between the first 3 digits and the last 3 digits. If you already have many records, create a calculation (number) field with this definition:
Left ( yourSerialNumberField ; 3 ) & " " & Right (yourSerialNumberField ; 3 )
You can use this second field with a space between the first 3 and last 3 for your project.