Question

which number does have a successor of any element in N​

Answer 1

Answer:

Union AUB: All elements that are either in A OR in B

The successor of A is AU{A}. Basically, the successor of the set A is the set A with the element {A} added to it.

Thus the successor of A contains one more element than the set A.

If the set A then contains n elements, then the successor of A contains n+1 elements.