ISTR doing Kant's approach to maths as part of philosophical logic, perhaps as background to Quine? (He cropped up at philosophy 'A'-level too, as I know from both studying and teaching it!) In a nutshell, he claimed that the analytic/synthetic distinction in logic did not correspond to the a priori/a posteriori disctinction in epistemology (or the necessary/contingent distinction in metaphysics), giving space for synthetic a priori knowledge (e.g. maths).

My favourite book on this sort of thing was Grayling's Introduction to Philosophical Logic, but there are probably newer books around, and I can't remember if Kant was mention much in it anyway!