Full Idea
According to 'in re' structuralism, a statement that appears to be about numbers is a disguised generalization about all natural-number sequences; the numbers are bound variables, not singular terms.
Clarification
'In re' means the structures are in the entities, rather than preceding them
Gist of Idea
Number statements are generalizations about number sequences, and are bound variables
Source
Stewart Shapiro (Philosophy of Mathematics [1997], 5.3.4)
Book Reference
Shapiro,Stewart: 'Philosophy of Mathematics:structure and ontology' [OUP 1997], p.166
A Reaction
Any theory of anything which comes out with the thought that 'really it is a variable, not a ...' has my immediate attention and sympathy.