Cross Reference Numbers Help

I am trying to figure out a quicker way of cross referencing numbers and hoping someone might be able to help. In column "A" is the number that groups the numbers in Column "B" together and Column "C" would be the result of the cross reference. Does anyone know a way I could make this more automatic? Thanks in advance for the help.

A B C
706 T013 T113,T713
706 T113 T013,T713
706 T713 T013,T113

708 T005 T105,T705
708 T105 T005,T705
708 T705 T005,T105