PA addresses are assigned from an LIR's allocation and are registered in the RIPE Database by the LIR.
IPV6 Allocation & Assignment Policy
The minimum size of an IPv6 PI assignment is a /48. If you need a larger assignment, you must provide documentation justifying the need for additional subnets or define special routing requirements for the additional sites for which they need an additional /48 independent IPv6 prefix.
RIPE IPV6 PI /48
Subnetting into /64s gives 65536 subnets, all of which have 1 /64s