The number two.
None, 53 is a prime number.
How about: 80
2 and 10 go into 40 and 50 evenly.
2
No numbers besides itself and 1 go into it evenly. The most common numbers to check are 2,3,4,5,6,9, and 10. THe rest you can figure out with times tables.
Only the number one.
There are no other whole numbers besides ' 1 ' and 19 that go into 19 evenly. That makes 19 a prime number.
Only the number one.
30
Least number is 40
These numbers go evenly into 20: 1, 2, 4, 5, 10, 20.
10 and 5 can go into 150 evenly.