NAAN: Name Assigning Authority Number
The NAAN part, following the "ark:" label, uniquely identifies the organization that assigned the Name part of the ARK. Often the initial access provider (the first NMA) coincides with the original namer (represented by the NAAN), however, access may be provided by one or more different entities instead of or in addition to the original naming authority.
The NAAN used in the ARK anatomy diagram, 13030, represents the California Digital Library. As of 2012, roughly a hundred organizations have registered for ARK NAANs, including numerous universities, Google, the Internet Archive, WIPO, the British Library, and other national libraries.
UC3/CDL maintains a complete registry of all currently assigned NAANs, which is mirrored at the (U.S.) National Library of Medicine and the Bibliothèque nationale de France.