Full Idea
Even Hume did not make empiricism so universal as to include mathematics in it.
Gist of Idea
Even Hume didn't include mathematics in his empiricism
Source
report of David Hume (Treatise of Human Nature [1739]) by Immanuel Kant - Critique of Practical Reason Pref
Book Reference
Kant,Immanuel: 'Critique of Practical Reason (Third edition)', ed/tr. Beck,Lewis White [Library of Liberal Arts 1993], p.13
A Reaction
Hume didn't actually exclude mathematics, and the notion of 'relations of ideas' is a pointer. Subsequent empiricist have offered promising accounts. Personally I like the idea that patterns are the key idea.