Is this possible? I assume this will involve some VB coding also:

Part Num Associated Part Num
123 456
789 5623
8521 6352
456 123
5478 9821
444444 AT256
5623 789


Formula in "C" that would find the mate and insert a "Pairing" number
So that the 1st and 4th rows would have a 1
and the 2nd and 7th would have a 2 etc