My main teacher for Buddhist meditation was a mathematician by training. He often used mathematical analogies in his teachings.

Buddhist "metaphysics" is kind of a bit unusual, it's not really like metaphysics as understood in Western philosophy.

Quoting from wikipedia -

Traditionally, metaphysics attempts to answer two basic questions in the broadest possible terms:

1. Ultimately, what is there?
2. What is it like?

But that's not the aim of Buddhist metaphysics.

Because - it's to do with experience. The logic is very valuable, helps you examine things closely. But the realization the Buddha taught about is something you have to see for yourself.  It's not a theory you have to aver :).

So, Buddhist metaphysics is much more to do with looking at things in different ways - in order to see that there are many ways of looking at things, and to not just understand that intellectually, but relate to it experientially in meditation and in your everyday life.

It's not at all based on the idea that at some point along the line through sufficient intellectual work, you are going to come up with a philosophical "theory of everything" rather like the scientific theory of everything that many scientists hope for.

In other words, it has the same questions, but without the expectation of finally answering them in a definitive way.

So where does that get us with numbers? These are just a few thoughts to share.

Yes, mathematical things like numbers, and like triangles and so on - they seem timeless and permanent according to some ways of looking at them in maths - the platonic approach.

But that's kind of paradoxical. If they really are timeless - how could we as beings in time ever be aware of them? If the number 7 is not imbedded in time, what would count as perception of it? And if the number 7 can never be perceived by humans, then what use is it in maths?

On the other hand, it doesn't seem to make much sense to say that the number 7 is something changeable and embedded in our world, and that for instance 3 + 4 = 7 is a purely contingent thing.

Perhaps this is telling us something. Buddhist teachings are just about looking directly at the truth and relating to it as well you can. And - sometimes the truths you find are a bit like a koan, something that you can't resolve through intellectual hard work. I think trying to understand the true nature of maths may be a bit like that too.