Full Idea
Frege had the insight that statements of number, like statements of existence, are in a sense second-level. That is, they are most fruitfully and least confusingly seen as ascribing a property not to an object, but to a concept.
Gist of Idea
Numbers are second-level, ascribing properties to concepts rather than to objects
Source
report of Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884]) by Crispin Wright - Frege's Concept of Numbers as Objects 1.iii
Book Reference
Wright,Crispin: 'Frege's Conception of Numbers' [Scots Philosophical Monographs 1983], p.10
A Reaction
This sounds neat, but I'm immediately wondering whether he is just noticing how languages work, rather than how things are. If I say red is a bright colour, I am saying something about red objects.