Incorrect. Abstract mathematical objects are not "encoded within the observable universe"
Sure they are. The set of concepts that humans can conceive are those which human brains, either directly or through tools like computers, can handle. Human brains evolved in the context usually called "the observable universe", so all concepts - including but not limited to abstract mathematical objects - we can think about are encoded within it, just in a real roundabout way. In other words, you can not know anything that isn't encoded in your causal past; even the very notion of abstraction only exists because it's inherent in the physical universe to such a degree that evolution encoded the principle into your brain.
And besides, the notion that math is supernatural - something that exists above physical reality, independent of it - is an unproven and probably unprovable assertion.