00000000599673210000000059967321 is a 16 character string. The last character is a check character for that string, calculated according ISO 7064 MOD 11-2. The string could be an ISNI according to ISO 27729.
In print an ISNI can be written as four blocks of four characters, in such cases often preceded by the string 'ISNI': ISNI 0000 0000 5996 7321
ISNI based link
- Wikimedia ("ISNI"=0000 0000 5996 7321)
ISNI based matchVIAF