So Anselmus's well-known 'proof' of God's existence stating that everything has a cause, therefore there must be a first cause, which is God, is indeed refuted by standard high-school mathematics (the theory of limits).

This theory establishes infinite regress without supposing infinite numbers. Indeed, we can do math without infinite numbers, with a single one, or with infinitely many. But the mere idea of infinite regress doesn't decide between them.

God isn't a math problem to solve, and the whole notion of having to prove God's existence is silly. Why not just cut to the chase and ask Him? Don't be a 'fraidy cat, comrade! "Ask, and ye shall receive. Seek, and ye shall find..." It may take a nanosecond for a response; it may take a decade or two. Or some measure in between. De Lawd have His reasons. A sincere, sustained quest won't be wasted time. Ditch the scrap paper and Just Do It. The sincere don't need Stupid Math Tricks.