IP addresses around the world are managed by IANA (Internet Assigned Numbers Authority)and five designated territory RIR’s (Reginal Internet Registries) for assignment to LIR’s (Local Internet registries) i.e., ISP (Internet Service Provider) and other larger organizations.
Provider Aggregatable (PA) and provider Independent (PI) are the two categories of IP Addresses. PI can be shifted to other ISP but PA cannot be shifted between ISP.
Most of the SME’s and organizations are assigned PA by their ISP. Since IP leasing is based on PI Addresses, ISP’s and Private organization’s acquire large quantity of PI Blocks from RIR and lease the IP’s to any individual or businesses.
Here is the comparison between the PA and PI