> That is possible with things like pi, which have recursive formulas to compute, but it's not easy for arbitrary numbers. It is possible for pretty much all t

> That is possible with things like pi, which have recursive formulas to compute, but it's not easy for arbitrary numbers. It is possible for pretty much all the numbers you could care about. I'm not claiming it is possible for all real numbers though (notice my wording with "express" and "represent"). In fact since this creates an equivalence between real numbers and functions on natural numbers, and not all functions are computable, it follows that some real numbers are not representable because they correspond to non-computable functions. Those that are representable are instead called computable numbers.