The atomic<shared_ptr<T>> and atomic<weak_ptr<T>> partial specializations are declared by <memory>, but are specified in Clause 31 [atomics]. Nothing in that Clause every mentions <memory>. It's not at all obvious which header you need for those specializations, unless you happen to find their declarations on the eighth page of of the <memory> synopsis in [memory.syn].

I think we should have a note in [util.smartptr.atomic] saying they're provided by <memory>.