http://www.google.com/search?q=%22042-68-4425%22
Apparently he has 16 of them.
(Don’t use Google):
http://www.dogpile.com/dogpile/ws/results/Web/obama%20social%20security%20numbers/1/114/TopNavigation/Relevance/iq=true/zoom=off/qlnk=1/_iceUrlFlag=7?_IceUrl=true