In mathematics, people also study infinite cardinal numbers. The first infinite cardinal number was named formula_1 (pronounced "Aleph null", "Aleph-zero" or "Aleph-naught") by Georg Cantor. formula_1 is the number of numbers that are in the group 0, 1, 2, 3, ... (which goes on forever). Both the set of natural numbers and the set of rational numbers are of size formula_1 (that is, they are both countable). 