Answer:
3
Step-by-step explanation:
Using listing:
[tex]1 \times 21 = 21[/tex]
[tex]3 \times 7 = 21[/tex]
No other factors are possible.
Hence, 1, 3, 7 and 21 are factors of 21.
Answer: 3
3 is the only number you can multiply to get 21. Example 3x7=21
