Full Idea
A set of things is located where the aggregate of those things is located, ...but a number is simultaneously located at many different places (10 in my hand, and a baseball team) ...so numbers seem more like universals than particulars.
Gist of Idea
Sets exist where their elements are, but numbers are more like universals
Source
Penelope Maddy (Sets and Numbers [1981], III)
Book Reference
'Philosophy of Mathematics: anthology', ed/tr. Jacquette,Dale [Blackwell 2002], p.349
A Reaction
My gut feeling is that Maddy's master idea (of naturalising sets by building them from ur-elements of natural objects) won't work. Sets can work fine in total abstraction from nature.
Related Idea
Idea 17824 The master science is physical objects divided into sets [Maddy]