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There are various choices for what a 'number' means:

* \\(\mathbb{N}\\) = set of all natural numbers = {0, 1, 2, ...}
* \\(\mathbb{N^+}\\) = counting numbers = {1, 2, ...}
* \\(\mathbb{Z}\\) = integers = {..., -3, -2, -1, 0, 1, 2, 3, ...}.
* \\(\mathbb{Q}\\) = rational numbers = all fractions p/q for integer p,q
* \\(\mathbb{R}\\) = real numbers = all limits of infinite sequences of rationals
* \\(\mathbb{C}\\) = complex numbers = all a + bi for real a,b