Full Idea
Pure mathematics is the science of the relations between any object whatever (relation of whole to part, relation of equality, property, unity etc.). In this sense, pure mathematics is seen by Husserl as formal ontology.
Gist of Idea
Pure mathematics is the relations between all possible objects, and is thus formal ontology
Source
report of Edmund Husserl (Formal and Transcendental Logic [1929]) by Victor Velarde-Mayol - On Husserl 4.5.2
Book Reference
Velarde-Mayol,Victor: 'On Husserl' [Wadsworth 2000], p.69
A Reaction
I would expect most modern analytic philosophers to agree with this. Modern mathematics (e.g. category theory) seems to have moved beyond this stage, but I still like this idea.