Assignment
AS numbers are assigned in blocks by the Internet Assigned Numbers Authority (IANA) to Regional Internet Registries (RIRs). The appropriate RIR then assigns AS numbers to entities within its designated area from the block assigned by the IANA. Entities wishing to receive an ASN must complete the application process of their local RIR and be approved before being assigned an ASN. Current IANA ASN assignments can be found on the IANA website.
Read more about this topic: Autonomous System (Internet)