By "numbers" do you mean digits and you want to add in leading zeroes like this?
A text field could be given this auto-enter calculation:
If ( Length ( self ) > 12 ; self ; Right ( "000000000000" & self ; 12 ) )
That keeps it all in one field. Note that adding or changing an auto-enter calculation to a field will not change the value in the field for records that were already present in the database.
A calculation field could also be used with a text result type.
If ( Length ( NumberField ) > 12 ; NumberField ; Right ( "000000000000" & NumberField ; 12 ) )
WIth this method, you'd enter a number into NumberField and the calculation field would then show the leading zero version.
Thank you! :)