The factors of a number are numbers that can divide the number without leaving any remainder.
Let's check the following numbers given.
Factors of 4 are:
1, 2, and 4 (This list includes all the factors of 4)
Factors of 10:
1, 2, 5, and 10 (This list includes all the factors of 10)
Factors of 5:
1 and 5 (This list includes all the factors of 5)
Factors of 21:
1, 3, 7, and 21.
We can see the list given 1 and 21 does not include all the factors of 21.
ANSWER:
21: 1, 21
