Publishing this number is illegal in the USA, because it's something of a commercial secret used to protect copyrights:

09:F9:11:02:9D:74:E3:5B:D8:41:56:C5:63:56:88:C0
or, decimal if you prefer:
13,256,278,887,989,457,651,018,865,901,401,704,640
or get it on a t-shirt (from the USA).

This number is the HD-DVD encryption key. If you know how to do it, it's possible to decrypt HD-DVD disks with this key, making them copyable, downloadable or whatever. As you might expect, there are lawsuits abound over the pond at the moment.