Given two numbers a and b, build a String that contains every number which is a factor of b, from a to b, inclusive. Preconditions: a < b for all inputs, a > 0.

A factor, also called a divisor, is a number that divides into another without leaving a remainder. The divisors of 10 are 1,2,5 and 10 (every number divides itself without a remainder).

For example if a is 3 and b is 10, the following decisions would be made.

Skip 3, 10 % 3 != 0.
Skip 4, because 10 % 4 != 0.
Include 5, because 5 is a factor of 10 (10 % 5 == 0).
Skip 6, because 10 % 4 != 0.
Skip 7, because 10 % 7 != 0.
Skip 8, because 10 % 8 != 0.
Skip 9, because 10 % 9 != 0.
Include 10, because 10 is a factor of 10 (10 % 10 == 0).

Thus, the overall result would be "510" for a == 3 and b == 10.