Unable to find any PTR-records for the specified domain/ip :(
Log
+000
Resolving PTR record of '72.21.192.0'
+201
ERRNo PTR record availible DNS server 'x2.amazonaws.com' raised an NotExistentDomain error, while beeing queried for PTR-records on domain '0.192.21.72.in-addr.arpa'.