It belongs to an infinite number of sets.
For example the sets of:
fractions
Irrational and transcendental
Any set of numbers that contain them! For example, they belong to the set {10, 11} or {10, 11, sqrt(2), pi, -3/7}, or {10, 11, bananas, France, cold} or all whole numbers between 3 and 53, or counting numbers, or integers, or rational numbers, or real numbers, or complex numbers, etc.
Integers. (This includes negative whole numbers.)
The integers. Also: the rational numbers, the real numbers and (depending on your definition) the complex numbers.
The set of numbers which 3 does not belong is the set of even numbers.
10 belongs to the set "natural numbers", but it can also belong to whole numbers, and rational numbers
Natural (counting) numbers; integers; rational numbers; real numbers; complex numbers. And any other set that you choose to define, that happens to include the number 4 - for example, the set of square numbers, or even numbers, the set of the numbers {3, 4, 5, 7, 14, 48}, etc, the set of numbers containing the letter o in their English name.
Counting numbers
Irrational numbers.
The set of even numbers
The numbers that belong to the series are the following: 1, 2, 5, 10, 13, 26, 29 and 48.
It belongs to the set of prime numbers
rational and prime numbers
Rational and Real numbers
mixed numbers
odd numbers, perfect square numbers