Classic Glenn Miller song, and still phone number of the Hotel Pennsylvania in New York City.

Of course, unless you either (a) know the area code off the top of your head (which really isn't too difficult for Manhattan), or like getting reamed with operator assistance charges, you'd probably prefer a more useful format for the phone number if you actually want to dial it:


Also the name of an extremely kickass a cappella group from University of Pennsylvania, better known as Penn Six.