Use !rdap-as to lookup Registration Data for an Autonomous System Number.
Registration data for Internet Protocol (IP) numbers are maintained by the Regional Internet Registries and contain registrant contact points along with technical details for each IP number registration.
Autonomous System Numbers (ASNs) are used in the Border Gateway Protocol (BGP) to identify an IP network managed or connected to the Internet by a single organization.
Usually, you do not need to prefix an Autonomous System Number with !rdap-as and just !rdap should work fine.