Concantenate cells using criteria or several if functions

Please reference my attached example spreadsheet. I am trying to concantenate cells based on criteria from other cells. In column A of the attached spreadsheet is a list of fake ssn some are duplicates. In column B their are seq numbers that are associated with the ssn in column A. Is their a formula to combine all the seq numbers in one cell that are associated with the same ssn. In column D i have typed out what I would want a formula to do for me.

Thanks,
Brian

Someone better than I may be able to come up with something, but I think it requires VBA. I use index,match, rows and columns but the results are over multiple rows. I found a post that is requesting the same info, and it required a VBA routine... Here's the link for that if you want to give it a shot. http://stackoverflow.com/questions/1...ultiple-values