To find the factors of a number, you first need to split that number into its prime factors. In the case of 15, this produces:
15 = 3x5
The next step is to note that every factor of the number (apart from 1) is the product of any combination of its prime factors. Thus, the factors of 15 are:
1, 3, 5 and 15.
All of them. Different numbers have different numbers of factors.
A whole number has an odd number of unique factors if and only if it is a perfect square. The perfect squares less than 10 are 0, 1, 4, and 9. Therefore, there are four whole numbers less than 10 that have an odd number of unique factors.
12 does not have any factors under 1, factors are whole numbers.
48 is divisible by ten factors. There is an infinite amount of numbers divisible by 48.
Three factors in common.
Four
All of them. Different numbers have different numbers of factors.
Six of them.
The limit is infinity if the factors do not have to be whole numbers. If you stipulate that the factors have to be whole numbers, then, yes, for each number, there is a limit to how many factors it has. For example, the number 4 has only 3 whole-number factors: 1, 2, and 4.
Four of them.
1,2,4,8,16, so 5
Six numbers. They are 1, 2, 4, 5, 10 and 20.
There are infinitely many such numbers.
14 (I think).
Four: 1 5 25 125.
A whole number has an odd number of unique factors if and only if it is a perfect square. The perfect squares less than 10 are 0, 1, 4, and 9. Therefore, there are four whole numbers less than 10 that have an odd number of unique factors.
12 does not have any factors under 1, factors are whole numbers.