Natural numbers.
1.18 is a number and number do not contain any sets (of any kind).
-10 belongs to the set of all integers denoted by Z.
173 belongs to the set of positive natural numbers and it also belongs to the set of prime numbers.
Infinity is not a number. There are different classes of infinity: The sets of natural numbers, integers, rational numbers all belong to the smallest class, with a cardinality of Aleph-null. The sets of irrational numbers and real numbers belong to the next higher level of infinity, with cardinality Aleph-One. Infinity can give rise to a very large number of apparent paradoxes - infinitely many of them?
Rational numbers
It can be element of: Rational numbers or Real numbers
real numbers, irrational numbers, ...
Natural numbers.
1.18 is a number and number do not contain any sets (of any kind).
17 belongs to the set of prime numbers
Irrational Numbers which are a subset of Real Numbers which are a subset of Complex Numbers ...
To any set that contains it! It belongs to {8}, or {8, sqrt(2), pi, -3/7}, or {8, bananas, France, cold} or all whole numbers between 4 and 53, or multiples of 2, or composite numbers, or counting numbers, or integers, or perfect cubes, or rational numbers, or real numbers, or complex numbers, etc.
The rational numbers, the real numbers and sets of higher order which contain the reals such as the complex numbers.
To any set that contains it! It belongs to {-8}, or {-8, sqrt(2), pi, -3/7, 99.3}, or all whole numbers between -43 and 53, or multiples of 2, or integers, or rational numbers, or real numbers, or complex numbers, or square roots of 64 or fourth roots of 4096 etc.
-10 belongs to the set of all integers denoted by Z.
integers and rational numbers