Unable to find any PTR-records for the specified domain/ip :(
Log
+000
Resolving PTR record of '72.13.121.0'
+315
ERRNo PTR record availible DNS server 'ns1.ghx.com' raised an NotExistentDomain error, while beeing queried for PTR-records on domain '0.121.13.72.in-addr.arpa'.