Well, don't think of it as a mathematical absurdity, because it's not about arithmetic or numeration at all. It's about love.
The most basic things we know about God are that God is One, and that God is Love. But Love can't be One in the most singleton solitary sense, because a "love of one" would be a profound egotism, a stuck-on-yourselfness which is not actually love at all, but quite a monstrous opposite.
So God who is Love is a Tri-unity. There is an inner back-and-forth of love, a giving and receiving and back again, a dynamism.
This has to do with the inner life of God within Himself, not as three "aspects" of one person, but as three Persons united in one Nature: a kaleidoscope.
And this is a Mystery, not because we can never understand any of it, but because we can never understand all of it.
And think: what could this possibly mean: that we were "created in the image and likeness of God"?
My response is that there's no possible way you can KNOW this. It must be taken by faith. Not that there's anything wrong with that but then there are those who get offended and act surprised if, God forbid, somebody asks a question about it. Not saying this describes you but I thought this is the FR a place to discuss these kind of things. :-)